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Repair, Don't Replace, Old Wood Windows

Posted by xoldtimecarpenter (My Page) on
Fri, Aug 6, 10 at 12:52

Is it my imagination or is almost all the discussion on this forum about replacement windows? I manage a remodeling company in the mid-west. We repair and/or replace windows as needed without prejudice either way. If a window can be repaired and that's what the customer wants, we repair it. If the customer wants it replaced, we replace it. It seems to me, however, that we are frequently asked to replace windows that don't need to be replaced, and we think replacing windows is a frequently bad economic and environmental choice. I know there are a lot of people on this forum that make their living replacing windows, and what I am about to say will probably drive them nuts. But it is a discussion that ought to be had, so here it is.

You may be unlucky and have old aluminum or steel windows on your old house, or even replacement vinyl windows from the 1970's or 80's. Most likely these cannot be repaired, and must be replaced. But if you are lucky enough to own a house with old wood double hung windows, you often have the choice to repair OR replace.

Most wood double-hung heritage windows can be restored and upgraded to rival the performance of a standard replacement window, and usually at a fraction of the cost. And there are other important advantages of repairing rather than replacing. You not only save on your own heating a cooling costs, which reduces waste and your carbon footprint on the planet, you also save the resources and energy cost required to manufacture new windows which considering what new windows are made out of, is not an inconsiderable savings. You also preserve, not just wonderful old-time workmanship, but the superb old growth wood from which your windows were made. We can't build windows like that any more. It's not that our craftsmen do not have the skill and experience. Any of our master carpenters or cabinetmakers could build a traditional window. But we can't get that dense, heavy old growth wood, and the new wood is ... well, we're pretty sure it's wood, but it's just not very good window wood.

Are Replacement Windows a Good Investment?

Before 1996, primarily as a consequence of the pervasive and unceasing marketing of replacement windows after the energy "crisis" of the 1970's (when gasoline prices jumped to an astounding $.80/gal. oh, for the good ol' days), it was nearly universally thought that replacement windows were vastly superior energy performers. But then the State of Vermont and the U.S. Army joined together to actually test the performance of restored heritage wood windows.

They repaired and restored 150 windows all over Vermont, then tested them against replacement windows in similar situations. What they discovered was an eye-opener. They found that the energy savings difference between restored old windows and new replacement windows amounted to just a few dollars a year. When a storm window was added to a restored window, the window/storm window combination actually outperformed many of the new thermal windows. These findings have been well supported by subsequent studies.

Keith Haberern, a professional engineer, in an analysis of New Jersey homes found that the annual energy savings of a modern replacement window over an old window in good condition is 626,000 Btu. How this translates into dollars depends on the cost of energy in your area. There are 1020 Btu, on average, in a cubic foot of natural gas, so the average saving to a natural gas customer is 614 cubic feet of natural gas per window. In most of my state, Nebraska, a cubic foot of natural gas sells for 1.2 (as of 2007). The energy cost savings, then, is a $7.37 per window per year.

At this rate, if you have 20 windows in your old house, your total annual savings would be about $147.40. The cost of a good quality thermal replacement window, installed, is about $500. You can pay a great deal more for a replacement window, but you will not find a quality window for much less. So, your window replacement cost will be around $10,000.

To pay for your replacement windows out of your energy cost savings would take a whopping 68 years. Odds are pretty good you won't live that long. But if you did, consider this: The life expectancy of a modern replacement window is only 15-40 years. So by the end of the 68 year payback period you will have replaced your replacement windows at least once, maybe twice. The net result, then, is that you will never actually recover your initial cost of replacement windows from energy savings alone.

Other studies have found even worse results. Researcher and energy consultant Michael Blasnik looked at actual energy bills of houses in upstate New York before and after replacement windows were installed and found the actual average annual savings per household was just $40.00 not per window but per house. Based on these findings, he concluded that it would take 250 years for the cost of the replacement windows to be repaid from energy cost savings alone.

Obviously there are reasons other than economic reasons to buy replacement windows. New window sashes tilt out for easy cleaning, they have several lock positions so the window can be opened slightly and still be secure (although old windows can be modified to do this). Old windows don't have these nice features. Or your old windows may have deteriorated to the point where they really can't be fixed although this is very unlikely. But if it is your intent to reduce your cost of heating and cooling to pay for your windows out of energy cost savings, think again. It won't happen.

While many replacement window manufacturers still claim reductions in household energy use of up to 35% after installing their replacement windows, most admit that these projections are based on hypothetical computer models, not actual field testing. When these claims have been field tested, little or no actual savings have been found. I have yet to find any window manufacturer's claims of energy performance to be backed up by actual field testing. If you know of one, please let me know.

Where an old window is restored and equipped with a good storm window, the old window system has been repeatedly shown to outperform the standard thermal replacement window. And it costs much less to restore an old wood window than it does to replace it with even an average thermal window.

Windows Built to be Repaired

Old wood windows were made to last for many generations. They were built to be repaired. The old-time craftsmen knew that their windows would last a good long time, but not forever. So they built windows that could be easily fixed when something finally did give way. Modern windows are not built that way. Most have a expected lifespan of less than 40 years, and other than replacing the glass, cannot easily be repaired. Frames are single integrated structures, as are sashes. In fact, in some modern windows, frames and sashes are completely integrated so literally noting can be repaired except some very incidental parts. But an old window is at least a dozen individual parts put together with joinery that can be undone It can be taken apart and any of the parts replaced individually without replacing the entire sash, or, worse, the entire window.

It can also be fully weatherstripped and insulated. We use a system that insulates sash weight pockets to between R-18 and R-22 probably better insulation than is in your walls. Using the right, long-lasting, materials, weatherstripping is actually fairly easy. Any competent window man (or woman) can do it in about an hour.

It can be a lot of work. But professionally restoring your old window is about half the price of replacing it with a new thermal window -- typically between $200 and $300 -- and wastes nothing. Old growth hardwood is saved from the landfill, and a lot of good old-time craftsmanship is preserved. If you can do it yourself, still more savings -- figure about $100 for materials.

Of course it is not yet as energy efficient as a new window. For that we are going to have to add a storm window. A good quality white aluminum storm window installed is about $80 in this area, and I doubt it is much more elsewhere. An upscale wood combination storm window from a company like SpenserWorks will cost a bit more (caveat: we have no connection to Spenserworks whatsoever).

If you already have storm widows, then you are just that much ahead, But assuming you don't, your cost to repair your old wood windows and add a good storm window is about $325.00 vs. $500 and more to replace them. This is a savings of $5,500.00 in a 20-window house. For your investment you get a window that should be good for another 100 years, while a replacement window is doing very well to last 40 years. Your window performance is just as good if not slightly better and you saved 45% of the cost of installing replacement windows.

I not alone in my opinion that repairing old wood windows is often a better choice than replacing them. The href='http://www.preservationnation.org/issues/weatherization/windows/additional-resources/nthp_windows_repair_replace.pdf'>National Trust for Historic Preservation has this to day:


Many window replacement manufacturers claim greater savings than actually occur. Since windows account for at most 25% of heat loss, the payback and time to recoup your investment in terms of energy savings could take between 40 and as much as 200 years, based on various studies. A study from Vermont show the saving gained from replacement windows as opposed to a restored wooden window with a storm is only $.60. The added problem is most replacement windows will not last as long as 40 years, much less over a hundred years. And some are being replaced only after 10 year of service."

Anyway, that's my view. Opposing argument is certainly welcome, but please, if you quote studies or statistics, back it up with a reference. Here are my references:

References


"Replacement Windows and Furnaces in the Heartland; Indiana's Energy Conservation Financial Assistance Program"
Center for Energy Research, Ball State University, Indiana, 1990. (Replacing windows without any other energy improvement results in an annual savings in energy costs of 1.4% per year.)

"What Replacement Windows Cant Replace: The Real Cost of Removing Historic Windows" Journal of Preservation Technology, 2005. (Replacement windows do not provide enough energy savings to justify the embodied energy cost of the new windows or the loss of authenticity.)


Testing the Energy Performance of Wood Windows in Cold Climates A Report to The State of Vermont Division for Historic Preservation, Agency of Commerce and Community Development"
University of Vermont, Vermont Energy Investment Corporation, U.S. Army Cold Regions Research and Engineering Laboratory. (The energy savings between replacement windows and restored wood windows based on a multi-year Vermont study was found to be insignificant.)


Follow-Up Postings:

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RE: Repair, Don't Replace, Old Wood Windows

While your suggestion has application in those situations where historic preservation is an issue and where the wood windows are in otherwise serviceable shape, this does nothing to address those windows that were manufactured and used in the last 30 or so years.

I was in a home last night that the windows have zero chance of being "restored" to any sort of serviceable condition for a reasonable price.

The lower rails on all of the windows where rotted and replacing that section of wood along with compensating for the shrinkage in the window for proper seal is an exhaustive process to say the least.

This is all before you begin to remotely address the thermal performance of the glass or the rot in the master frame of the window.

Perhaps some year ranges on the windows would be helpful for potential customers reading this thread.

Most of everything made in the last 30+ years is not worth saving. I am a huge advocate of restoration, however, the engineered obsolescence in most of the building materials of the last 3-4 decades eliminates that possibility altogether.

You claim of a payback periods of 68 years on replacement windows is suspect to say the least. While the claim of 40% savings isn't worth the paper that it is written on, I have seen whole house airflow reductions of 28% after just window replacements. You couple that with added thermal efficiency built into the window and you have a window that will likely save you around 25 - 30% on your utilities. That can translate into a sub-15 year payback period.

All of the studies you are posting are in regards to historic wood windows and it is important for a consumer to understand that distinction.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

Thanks for your response. A couple of things I need to clear up. First, my remarks are not limited to windows of historical significance - which is what I assume you mean by "historic wood windows". They apply to virtually all wood windows built before 1970, the so-called "heritage" windows. You noted that windows built within the last 30 years are usually not worth replacing. I said the same thing in my post, and I agree with you. Most are just junk. Unfortunately, most of the windows built today are still just junk.

There is almost no manufactured windows made today that will last over 50 years because of the vinyl, rubber and other degradable materials used in their manufacture. Sash weight balances last forever, vinyl and spring balances used in new windows barely make 20 years.

As to payback periods -- there are exactly no, none, zip, nada field studies that have found a payback period of less than 50 years. If you know of one, I'd like to read it. I'm pretty sure I read them all, but I could have missed one or two.

Manufacturers can, of course, and do, claim any payback period they like, and can usually back up the claim with a fairly convincing computer model or two. But hypothetical computer models are not real world results, and real world results, so far, have shown the computer models to be, at best, wildly optimistic. Any time I have challenged a manufacturer to prove his model, the result is more back-pedaling than a French Army retreat.

Finally, air infiltration and window thermal performance are different things. I can take a house full of old air-leaky windows and replace put plywood over the window openings, seal with caulk and foam and get almost no air infiltration. Any time you replace old windows with new, you carefully foam and caulk and as a result there will be little air leaking around and through the windows. You can do the same thing to the existing old windows -- it's called weather-sealing, and once it is done they too show almost no air infiltration in pressure tests. So if you replace windows because they leak air instead of weather-sealing them, you customer has in effect paid a lot for windows he did not need. What he needed was weather-sealing.

If old windows can be weather-sealed as well as replacement windows, and the thermal performance of well-restored old windows with storms is the same as or better than new replacement windows, why would you replace?

I agree that some wood windows are so bad they cannot be economically repaired. But in 40 years I have seen only a dozen or so houses where this was true, and most often the houses themselves are so deteriorated that fixing the windows is the very least of the problems.

You gave the example of windows you saw recently with rotten sills. Rotten sills can be replaced fairly easily, and sashes that have shrunk so they are loose in their frames can be weatherstripped like new. So if the windows are otherwise in good shape, these minor problems suggest to me that the windows should be repaired, not replaced.

Understand, I am not opposed to replacing windows. We replace hundreds of windows every year. But we prefer to repair when we can. It saves the customer money, it helps the environment, and it preserves the architectural integrity of the structure. We think all of these are good things to do.


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RE: Repair, Don't Replace, Old Wood Windows

You will never get payback periods quoted from a manufacturer because every home is different. As I mentioned, I have personally observed a minimum of a 26% reduction in air leakage as well as 2X fold increase in the R-Value. The combination of these two factors will likely translate to a 30%+ reduction in this homeowners case.

I have copied this post from my buddy Oberon.

He has forgotten more about energy efficiency that I can hope to assimilate in my life.

A single lite of 1/8" glass has an R-value of slightly less than 1. Many folks simply round the R-value of single glass to 1 for convenience, but not the 1.67 that you stated.

"...even the worst walls (2x4 construction with fiberglass batt insulation) have an R-value of about 20..."

Fiberglass batt at 3-1/2" has an R-value of 13. However, add studs at 16" on center and per ASHRAE the total R-value of a 2x4 wall drops by approximately 18% to R 10.7. Add siding, sheathing, and interior wall covering and you may reach an R12 to R13 depending on materials used, but not an R20.

"No window comes anywhere close to matching the R-value of a wall..."

Well, there are new windows on the market that have R-values in the 8 to 10 range which I would suggest is fairly close to the value of the 2x4 wall with fiberglass batts that you mentioned earlier.

"...and the effect on the R-value (energy efficiency) of your wall would be very small."

Define "very small"?

To keep it simple, imagine a single 100sqft wall 2x4 stud wall in a home with fiberglass batt insulation and an R-value of 12 not including any windows or doors - yet.

Add a 10sqft window with an R-value of 3.63 (from your post). Convert the R3.63 to U factor of .275 (U = 1/R) for energy performance computations.

Wall = R12 or U.083
Window = U.275
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.275 = 2.75
7.5 + 2.75 = 10.25/100sqft = U.1025 or overall wall R value of 9.75.

Now if we consider a single pane window with an R1.67 which is too high, but we will use it for this illustration. U-factor of that window is .6.

Wall = R12 or U.083
Window = U.275
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.6 = 6
7.5 + 6 = 13.5/100sqft = U.135 or overall wall R value of 7.4

Using the percentage change formula = (x-y)/y*100 = Z%, and the numbers from the computations - (9.75-7.5)/7.5*100 = 30%.

So, while the comparison of window to window energy performance numbers results in an R-value increase that a little better than doubles using the numbers that you posted (which is significant in itself); by increasing the energy efficiency of the window from R1.67 to R3.63 the overall wall efficiency in the example will be improved by 30% - simply by using the more efficient window.

Picture an entire home. I would probably not consider that to be "very small".

"Storm windows would net you the same energy efficiency as the double-pane+Low-E+Argon windows"

Not unless the storms are also double pane + LowE + argon, they wont.

A clear glass dual pane IG window will have the same center-of-glass R-value as a single pane with storm. But, add the bells and whistles and the window with LowE and argon will significantly outperform the single pane and storm.

"Bendheim crafts truly accurate reproduction glass by simply using the old manufacturing procedures."

Actually, Bendheim doesnt "craft" raw glass. While Bendheim does do some in-house fabrication, they are primarily a glass importer. Restoration and vintage glass comes primarily from Germany where it is manufactured using the same techniques that were used in days past.

"When it comes to the heating and cooling costs of a building, windows don't make a significant impact"

You really need to get that data to the Department of Energy as soon as possible since their energy policies certainly dont take your information into account.

In fact, in cooling dominated climates there are studies showing 35% (or better) overall home energy performance improvement when comparing clear glass dual pane to IGs including solar-blocking LowE coatings and argon.

In heating dominated climates the improvements tend to be a bit more modest; but improvements of 30% (or better) have been documented.

Again, these numbers are from real homes in real conditions and are not laboratory or computer simulations and these are whole-house, total energy usage numbers, not simply comparing windows to windows. A single lite of 1/8" glass has an R-value of slightly less than 1. Many folks simply round the R-value of single glass to 1 for convenience, but not the 1.67 that you stated.

"...even the worst walls (2x4 construction with fiberglass batt insulation) have an R-value of about 20..."

Fiberglass batt at 3-1/2" has an R-value of 13. However, add studs at 16" on center and per ASHRAE the total R-value of a 2x4 wall drops by approximately 18% to R 10.7. Add siding, sheathing, and interior wall covering and you may reach an R12 to R13 depending on materials used, but not an R20.

"No window comes anywhere close to matching the R-value of a wall..."

Well, there are new windows on the market that have R-values in the 8 to 10 range which I would suggest is fairly close to the value of the 2x4 wall with fiberglass batts that you mentioned earlier.

"...and the effect on the R-value (energy efficiency) of your wall would be very small."

Define "very small"?

To keep it simple, imagine a single 100sqft wall 2x4 stud wall in a home with fiberglass batt insulation and an R-value of 12 not including any windows or doors - yet.

Add a 10sqft window with an R-value of 3.63 (from your post). Convert the R3.63 to U factor of .275 (U = 1/R) for energy performance computations.

Wall = R12 or U.083
Window = U.275
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.275 = 2.75
7.5 + 2.75 = 10.25/100sqft = U.1025 or overall wall R value of 9.75.

Now if we consider a single pane window with an R1.67 which is too high, but we will use it for this illustration. U-factor of that window is .6.

Wall = R12 or U.083
Window = U.275
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.6 = 6
7.5 + 6 = 13.5/100sqft = U.135 or overall wall R value of 7.4

Using the percentage change formula = (x-y)/y*100 = Z%, and the numbers from the computations - (9.75-7.5)/7.5*100 = 30%.

So, while the comparison of window to window energy performance numbers results in an R-value increase that a little better than doubles using the numbers that you posted (which is significant in itself); by increasing the energy efficiency of the window from R1.67 to R3.63 the overall wall efficiency in the example will be improved by 30% - simply by using the more efficient window.

Picture an entire home. I would probably not consider that to be "very small".

"Storm windows would net you the same energy efficiency as the double-pane+Low-E+Argon windows"

Not unless the storms are also double pane + LowE + argon, they wont.

A clear glass dual pane IG window will have the same center-of-glass R-value as a single pane with storm. But, add the bells and whistles and the window with LowE and argon will significantly outperform the single pane and storm.

"Bendheim crafts truly accurate reproduction glass by simply using the old manufacturing procedures."

Actually, Bendheim doesnt "craft" raw glass. While Bendheim does do some in-house fabrication, they are primarily a glass importer. Restoration and vintage glass comes primarily from Germany where it is manufactured using the same techniques that were used in days past.

"When it comes to the heating and cooling costs of a building, windows don't make a significant impact"

You really need to get that data to the Department of Energy as soon as possible since their energy policies certainly dont take your information into account.

In fact, in cooling dominated climates there are studies showing 35% (or better) overall home energy performance improvement when comparing clear glass dual pane to IGs including solar-blocking LowE coatings and argon.

In heating dominated climates the improvements tend to be a bit more modest; but improvements of 30% (or better) have been documented.

Again, these numbers are from real homes in real conditions and are not laboratory or computer simulations and these are whole-house, total energy usage numbers, not simply comparing windows to windows. A single lite of 1/8" glass has an R-value of slightly less than 1. Many folks simply round the R-value of single glass to 1 for convenience, but not the 1.67 that you stated.

"...even the worst walls (2x4 construction with fiberglass batt insulation) have an R-value of about 20..."

Fiberglass batt at 3-1/2" has an R-value of 13. However, add studs at 16" on center and per ASHRAE the total R-value of a 2x4 wall drops by approximately 18% to R 10.7. Add siding, sheathing, and interior wall covering and you may reach an R12 to R13 depending on materials used, but not an R20.

"No window comes anywhere close to matching the R-value of a wall..."

Well, there are new windows on the market that have R-values in the 8 to 10 range which I would suggest is fairly close to the value of the 2x4 wall with fiberglass batts that you mentioned earlier.

"...and the effect on the R-value (energy efficiency) of your wall would be very small."

Define "very small"?

To keep it simple, imagine a single 100sqft wall 2x4 stud wall in a home with fiberglass batt insulation and an R-value of 12 not including any windows or doors - yet.

Add a 10sqft window with an R-value of 3.63 (from your post). Convert the R3.63 to U factor of .275 (U = 1/R) for energy performance computations.

Wall = R12 or U.083
Window = U.275
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.275 = 2.75
7.5 + 2.75 = 10.25/100sqft = U.1025 or overall wall R value of 9.75.

Now if we consider a single pane window with an R1.67 which is too high, but we will use it for this illustration. U-factor of that window is .6.

Wall = R12 or U.083
Window = U.6
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.083 = 7.5
Window = 10 sqft x U.6 = 6
7.5 + 6 = 13.5/100sqft = U.135 or overall wall R value of 7.4

Using the percentage change formula = (x-y)/y*100 = Z%, and the numbers from the computations - (9.75-7.5)/7.5*100 = 30%.

So, while the comparison of window to window energy performance numbers results in an R-value increase that a little better than doubles using the numbers that you posted (which is significant in itself); by increasing the energy efficiency of the window from R1.67 to R3.63 the overall wall efficiency in the example will be improved by 30% - simply by using the more efficient window.

Picture an entire home. I would probably not consider that to be "very small".

"Storm windows would net you the same energy efficiency as the double-pane+Low-E+Argon windows"

Not unless the storms are also double pane + LowE + argon, they wont.

A clear glass dual pane IG window will have the same center-of-glass R-value as a single pane with storm. But, add the bells and whistles and the window with LowE and argon will significantly outperform the single pane and storm.

"Bendheim crafts truly accurate reproduction glass by simply using the old manufacturing procedures."

Actually, Bendheim doesnt "craft" raw glass. While Bendheim does do some in-house fabrication, they are primarily a glass importer. Restoration and vintage glass comes primarily from Germany where it is manufactured using the same techniques that were used in days past.

"When it comes to the heating and cooling costs of a building, windows don't make a significant impact"

You really need to get that data to the Department of Energy as soon as possible since their energy policies certainly dont take your information into account.

In fact, in cooling dominated climates there are studies showing 35% (or better) overall home energy performance improvement when comparing clear glass dual pane to IGs including solar-blocking LowE coatings and argon.

In heating dominated climates the improvements tend to be a bit more modest; but improvements of 30% (or better) have been documented.

Again, these numbers are from real homes in real conditions and are not laboratory or computer simulations and these are whole-house, total energy usage numbers, not simply comparing windows to windows.


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RE: Repair, Don't Replace, Old Wood Windows

I love that someone is championing the cause of the older wood window! We purchased our first home 2 years ago, a 1949/50 cape cod. The windows in this house are unusually huge, which we love. 10 of the 16 windows were replaced with newer (and HORRIBLE) windows, with the front and east side still being the original wood with 8 panes in each half (charming!). I cannot say enough for how amazing these windows are - you cannot feel heat nor cool through them and the look just screams cape cod. The newer windows are at least 8 years old but the sealing is poor, the top panel is constantly sliding down with no way to keep it back up, and just all around not as classy.

Amway, all that to say someday we'd like to have them re-glazed professionally and just repaired in general. I'm glad to know it's not only a possibility, but is what was originally intended.

Thank you again for this post - the charm of these windows is enough for me to keep them forever :)


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RE: Repair, Don't Replace, Old Wood Windows

Ivoryandnoir,

Don't know where you live, but I'll bet there is an OldTimeCarpenter in your area who can build 10 old wood windows to replace your new replacement windows for a reasonable price. Add storm windows from SpenserWorks ( have no connection to this company) to complete the look and you will have windows you can treasure.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington

This Oberon fellow sounds very smart, but all his mathematical models do not make up for the fact that the models do not reflect the real-world results found in actual field studies. This is because these static models measure only the heat loss through conduction and to a lesser extent, radiation. Most heat loss is not through conduction, it is through air leaks and convection. No static model takes into account convection because they all assume that the air on both sides of the window is absolutely still. In fact, it's not. It's moving constantly and with that movement goes heat.

A window, as any insulation expert will tell you, is just a thermal hole in an otherwise well-insulated wall. Air seeks out those thermal breaks through the process of convection.

In simplified fashion convection works like this: Warm air in the room hits the colder window glass. It loses some heat to the glass, thereby getting cooler. Cold air is heavier than warm air, so it falls. Warm air rushes to fill the vacuum cause by the falling cooler air and a convention current is formed that constantly moves heated air to the window where it loses heat to the glass. On the outside, moving air contributes to the process by picking up heat from the glass, which is warmer than the outside air, keeping the glass cold so the convection process on the inside can never stop as long as the outside is colder than the inside air.

This is the source of those mysterious drafts in winter -- the ones you cannot figure out where they come from. This is where they come from.

Naturally a well-insulated and leak free window is going to convey less heat than a leaky window that is poorly insulated, but not as much as the static models suggest because they simply do not account for convection.

The U-value ratings touted by window manufacturers are developed from tests that specifically exclude air loss and convection. In the testing environment convection and air loss are tightly controlled so there is no measurable convection or air loss effect. So any U-value rating says nothing about convection effects, only the effects of conduction and, to some extent, radiation.

To model convection effect takes a pretty powerful computer because heated air is drawn to the window from everywhere in the room in many currents and the currents shift constantly. Every time you enter, leave or move around in the room, the currents shift. Every time you turn on a light or the furnace comes on, the currents shift. Modeling convection in the real world would be a daunting task.

But you can measure the effects of convection, and the effects in the real world are measured through field performance studies. These show uniformly that when dual pane thermal replacement windows are compared to tight-fitting single-pane windows for actual performance, there was no statistical difference between the two window types, although the static models suggest that there should be.

I have no doubt that as you stated your have seen dramatic improvements in heat retention when old, loose, leaky problem windows were replaced with carefully installed, weather-sealed, replacement windows. But my question is, if the old, loose leaky problem windows were repaired to eliminate leaks, then supplemented with a good storm window, would the improvement have been any less dramatic? Field studies such as the on-going Vermont study suggest it would not be. You would get the same dramatic improvement with the restored windows -- in fact the restored old windows would perform about 15% better.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

You are right about Oberon...he is extremely smart. I will copy him on this post to see what his feedback is.

For future discussions, let go ahead and assume that air infiltration is maintained as a constant. Obviously, a leaky window must be replaced or retrofit to be tight. I know that air infiltration/exfiltration is more often a larger issue than fenestration when it comes to residential energy efficiency.

Back to your post, please post up what field performance studies......."show uniformly that when dual pane thermal replacement windows are compared to tight-fitting single-pane windows for actual performance, there was no statistical difference between the two window types".....

What test shows that? If that is the case, what is the point of any of the advances in window technology? Double pane, triple pane, R-6, R-11, etc windows are worthless then when compared to a single pane wood?

I will acknowledge that the NFRC thermocouples testing is not representative of the energy flow in a dynamic environment, however, it is the best they can use to establish a standard with which to measure products. Depending on season, energy loss/gain will be driven in majority by different pathways. Radiation in the summer and conduction and convection in the winter.

Even if we assume that convection is the dominate pathway for energy to leave or enter the structure (which is definitely debatable if not out right false depending on the climate region) what do you think drive convection?.... Differential temperatures is what drives convection. Differential temperatures are mitigated by limiting conduction and radiant losses. By your math, insulating walls is an overhyped building approach if convection is the culprit.

If I am in Texas and standing in front of a window, is that convection I am feeling?

Argon, Low-e, and insulated frames are all integrally important into the window efficiency equation. How can you (or the Vermont study) claim that a wood window out performs a replacement by 15%.

If I am looking at an older home that has original wood windows (figuring them to be air tight) they are an average of about R-1.25. If we figure an 80/20 split of walls (at an R-10) to window, the average wall R-Value between that original wood window and a new efficient double pane with is pretty significant.

Old wood (R-1.15) = average R-Value of 3.94
Old wood with storm (R-1.85) = average R-Value of 5.32
Insulated window (R-4.00) = average R-Value of 7.69

85% improvement when compared to single pane wood
45% improvement when compared to single pane storm combo

Where again did you come up with the restored windows being 15% better?

Again, I want to be clear for the record that I like the idea (when feasible) or restoring historic windows as opposed to replacements. I truly do. Restored Wood windows, combined with storm windows (with hard coat low-e) can be sufficiently thermal systems. I just think that some of your science is questionable.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

You make some excellent points, so let's see if I can deal with them one by one.

First, obviously I am talking about window performance in a predominantly heating area of the country like Vermont or Nebraska. And I am talking about heating, not cooling. In summer or in predominantly cooling areas radiation plays a larger role in heat transfer. For the time being let's stick to heating to avoid getting unduly complex by mixing heating and cooling.

You said:

'please post up what field performance studies......."show uniformly that when dual pane thermal replacement windows are compared to tight-fitting single-pane windows for actual performance, there was no statistical difference between the two window types'.....

Ok, first here is one report from the study: Testing the Energy Performance of Wood Windows in Cold Climates A Report to The State of Vermont Division for Historic Preservation, Agency of Commerce and Community Development. This report goes on at length about the study methodology and other stuff that is really of interest only to scientists, but the conclusions are enlightening. Here is a recast summary of what was found.

Start with a restored, painted window with a new storm. This is the window that we will call the "restored window" against which all other windows are compared. The question posed by this research was how much could be saved in energy cost by upgrading this window.









Window DescriptionHeating Cost Savings
Restored window---
Replacement sash with storm-0.80
Low-e replacement sash with storm2.57
Double-pane replacement sash-0.37
Low-e double pane replacment sash-3.13
Replacement double-glazed window inserts1.07
Replacement low-e double pane window4.45


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RE: Repair, Don't Replace, Old Wood Windows

Its always a pleasure to see a discussion like this one about restoration versus replacement staying civil and even polite. All too often it degenerates into something unpleasant.

I am very familiar with all of the references that were listed regarding restoration versus replacement. I first read the Vermont study probably 10 years ago give or take.
Simple definitions of heat transfer

Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole.

Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat carrying energy with it.

Radiation is heat transfer by the emission of electromagnetic waves that carry energy away from the emitting object.

Carpenter, your illustration and explanation of heat transfer by convection is really good and it is correct with one exception the actual heat transfer thru the window is conductive not convective. When you have a warm side and a cold side of any material and you have heat transfer thru the material (in this case the window glass and sash) then you are talking about conduction.

How to limit both convection and conduction thru a material?
Increase the materials insulating value.

How to do it with a window?
You add a second piece of glass adding a storm window to an existing single pane window or changing the single pane to dual pane.

Glass does not insulate, air insulates. Totally dead air has an insulating value of about R5. Moving air (convection) has a much lower R value. This is why a single pane with a storm with a 3" space between the lites will not have better R value than will a dual pane with " between the lites. The convective currents in the 3" airspace in the single pane with storm lower the insulative value of the airspace to a level that is very close to the " in the sealed IGU or insulating glass unit or dual pane. This is real life, this is measurable.

And after all that is said, the primary heat gain or heat loss factor thru windows is radiant. Depending on the specific conditions more than 60% of heat loss or gain thru a window is radiant and I am considering conduction, convection, and infiltration (at .3 cfm) when using that percentage.

Infiltration, whether between sash/frame or between frame/stud cavity or wherever else it may be is a wild card. But it is something that can be addressed and by closing off infiltration routes by tightening up a loose window a huge benefit can be achieved. But it will not stop heat loss or gain thru the glass which per the Vermont report (for example) was the primary factor in window performance, not infiltration. The Vermont report mentions specifically that during their data gathering they found that heat loss thru the glass (radiant and conduction) exceeded infiltration.

Some real numbers:

When it is 0F outside and 70F inside and you have very little wind, the interior surface temperature of a single pane of glass is going to be right about 16F; which is definitely going to contribute to those convection currents.

Add the second lite, be it storm or dual pane and you increase the interior glass surface temperature to 44F. That is a very significant improvement. And once again, that is not simulation, it is real measurement data.

Add the LowE coating in a dual pane and the temperature of the glass surface increases to the mid 50s F (53F 57F) depending on the coating and the glass surface that has the coating.

Quick Rule-of-Thumb for Glass Performance Options
Single Pane R1 or U1

Single Pane and storm window R2 or U.5
Dual Pane, clear glass R2 or U.5
Dual Pane, LowE coated R3 or U.33
Dual Pane, LowE coated, Argon fill R3.5 or U.29

Triple Pane or dual pane with storm, all clear glass R3 or U.33
Triple Pane, one lite LowE coated R4 or U.25
Triple Pane, two lites LowE coated R5 or U.20
Triple Pane, two lites LowE coated, argon fill R6 or U.17
Triple Pane, two lites LowE coated, krypton fill R6.5 or U.15

Keeping in mind that these are general glass-only numbers that will vary depending on factors such as airspace width, type of LowE coating used, and other specific construction details.

To use an extreme example of real world performance - measured, documented, refined, and so on - consider the German Passivhaus concept.

There are over 10,000 buildings worldwide that have been built to passivhaus criteria. One of the most critical areas of passivhaus design is the windows, and there are no single pane /storm windows used in passivhaus design because they simply wouldnt come close in any way to meeting the criteria of this very rigid program. Windows are chosen based on specific design criteria of both solar heat gain and heat retention radiant and conductive heat transfer.

And passivhaus aside, there are literally millions of people in this country and elsewhere that are extremely happy with their replacement windows; just as there are many who are absolutely thrilled with their restored windows.

Like Windows on Washington, I very much favor restoration of historic windows to replacement no doubt at all. I have seen some amazing homes or other buildings totally butchered by uncaring or uninformed "updates". But I have also seen some run down older homes and buildings that were not architecturally significant that have been improved by updating including new windows.

And while restoration can be a lot more economical than replacement, its not always. A little research in this site and others will show more than a few posts from folks who had serious sticker shock when they were told what it would cost to refurbish their windows. In some cases the cost of restoration exceeded the cost of replacement which makes the decision much more difficult for the homeowner.

Bottom line is that whether to replace or restore is up to the homeowner. Hopefully, depending on circumstances they do the proper research before making an informed decision. Unfortunately, that isnt always the case.

Replacing perfectly good single panes with a cheap clear glass dual pane simply to "save money" is not an informed decision, and I know that window folks like Windows on Washington and Skydawggy share that opinion because I have seen their comments on it here and elsewhere.

But, higher end replacement windows with the "bells and whistles" will save energy and money over restoration no matter how much time and effort is put into the restoration. And once again, in the right circumstances restoration may very well be the right decision.

And while there is an argument for longevity of single pane and sash versus newer, "engineered" windows, there is also the argument that the pyramids will outlast a modern skyscraper, but that doesnt mean that the pyramid is a better idea, it is simply different.


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RE: Repair, Don't Replace, Old Wood Windows

Whoops! Looks like my last post was truncated and scrambled a little. Maybe this BB does not support tables.

I will delete this and start over. Does anyone know how to delete a post or do I have to contact the administrator?

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Oberon,

Loved your post. But as for being civil, I have never found a reason to be uncivil unless someone was actually shooting at me.

Actually we are both talking about the same thing. I disagree with little you have said -- and most of my disagreement is one of emphasis.

For example, I do not agree that heat transfer through a window is conductive. It is conductive through the glass, but otherwise it is convective.

Assuming a dual glass pane window: Convection carries warm air to the inside glass where it gives up heat and falls thus creating a convection current that continues to give up heat to the glass. The glass now transfers the heat to the air on the opposite side of the glass by conduction through the glass. On the inside of the glass it is picked up by another convection current that is constantly flowing between the two panes. This current picks up heat from the inside pane and transfers it to the cooler outside pane. The outer pane then conducts the heat to the cold outside air. Only the transfer through the glass is conductive. All of the remaining transfer is by convection. Of course, I am completely ignoring radiation and air exfiltration in this example. If the space between the glass panes is filled by argon or krypton, convection still occurs although it may be slowed down a bit.

While it is true that dry, still air is a good insulator, air is seldom dry and never still. In walls, insulation can be used to break up the convection currents between the inside wall covering and the exterior sheathing. That cannot be done in windows because you have to leave the glass transparent -- otherwise, what's the point of a window? If it was not for this pesky little problem, insulating windows would be easy.

Air flows inside an uninsulated wall cavity creating convection currents that efficiently -- too efficiently -- move heat from the warm inside to the cold outside. What wall insulation does that makes it effective is turn one large convection current inside your walls into hundreds or thousands of tiny convection currents. It is these air pockets, little convection cells, formed by the insulation that make it insulation. Multiplying the number of convection cells that heat must navigate slows down the transfer of heat -- but, unless you suspend the laws of thermodynamics, nothing can actually stop it. Eventually heat will find its way out of your house. But by slowing it down through insulation and weather-sealing, you get to use it in your house longer and you have to add heat less often to make up for the loss. This is what saves energy dollars -- adding heat less often to make up for the loss -- and why wall and attic insulation is a very good idea.

But going back to my original argument. If a house has old wood windows, particularly double hung windows, they may be worth saving. In every instance, certainly not. But in most cases, yes. If they are restored and coupled with a good storm window, then their thermal performance is for all practical purposes equivalent to a dual-glazed replacement window -- or so close that it makes little difference. If the annual heat cost savings per window between a restored old wood window and a new thermal is $4.00 or less (as was found in the Vermont study) and the difference in cost between restoring and replacing is $3,000 or more (as is typical around here), it makes no economic sense to replace. Of course the cost of repairing old windows can be very high. Almost any old window can be saved if one is willing to spend enough time and resources, but our rule of thumb is that if the average cost per window is greater than $300.00, then there is no economic advantage to repairing over replacing. We can, however, make a window, including glass, for about %500.00. So if someone is charging more than this to restore a typical old window, there is something wrong somewhere.

The cost of replacement windows can be much, much higher. We can get a good quality low-e dual glazed thermal in vinyl for around $500.00 installed, but add argon or krypton (especially krypton) to a wood or wood clad window with triple glazing and I don't think I've seen a price much less than $800, my cost, and most are far more.

Super windows such as those specified for the various German Passive Houses are expensive enough to make you gasp. But these are a special case. Here the objective was essentially to create a house that uses no outside energy at all -- at least if my memory serves, this was the objective. Naturally some sort of super window is needed in that situation. But these are experimental dwellings -- and horribly expensive -- definitely not affordable housing. For the typical house nothing like that is even remotely required.

I'm am not saying restore all old windows, nor am I suggesting that replacing old windows is always bad and should be avoided. What I am saying is that if your old wood windows can be restored, you have a choice that will not severely impact your energy costs. A restored wood window's energy performance will compare favorably to a moderately priced replacement thermal window, and if there is any difference it is minuscule compared to the total energy consumption of your household.

Minnesota public power has published what they call the "pyramid of conservation" which ranks energy savings steps in terms of payback. The pyramid can be viewed at Minnesota Power. The pyramid illustrates the basic rule of conservations: simple, inexpensive steps to conserve energy have the largest payback. As energy conservation measures grow more complex and more expensive, payback decreases.

Simple things like turning the thermostat down, replacing incandescent light bulbs with compact fluorescent bulbs, caulking and air sealing, and banishing vampire power loss have the most payback in terms of energy savings. Midway up the pyramid are wall and attic insulation -- I would have though they would be lower -- but they're not. Almost at the top are energy efficient furnaces and heat pumps. Window replacement is next to the top, just under solar power and windmills. Replacing windows has one of the lowest paybacks. Many would argue, and I agree with them, that window replacement just does not produce enough energy savings to pay off the initial investment during an average person's lifetime.

Better you should put your energy conservation dollars into something lower down on the pyramid -- a nice high-efficiency hot water heater will save more energy dollars than any but the most efficient replacement windows, and cost a whole lot less -- about $9,000 less in a typical home.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

I agree, and thanks, I enjoy your posts as well.

If a home's windows are in poor shape then refurbishing or restoring them to their orginal condition is always a good idea - no exceptions. But it may or may not be the best idea.

Depending on circumstances replacement may or may not be the best idea. There are circumstances where replacement is going to be better than refurbishing and there are going to be circumstnaces where refurbishment or restoration is the better idea.

And that is about as wishy washy as I can be.

People need to keep in mind that clear glass dual pane windows were developed to achieve single pane/storm performance in a single sash rather than separate window/storm combination.

First generation LowE coatings were developed to give triple pane performance in a dual pane window.

Passivhaus design really isn't that much more expensive than conventional design. The advantage of passivhaus is that while the structure and insulation requirements are a lot more expensive, there is significant savings in HVAC which offsets a good bit of the extra basic construction/insulation costs.

Windows used in passivhaus design are very good, and some people do use the term "super window" to describe them. But the principles used to design and build them are not remarkably special and could be much more common if the market demand is there.

The primary advantage over windows more readily available is in the frame and sash design/construction. The glass package in these windows is available if a consumer knows what to look and ask for.

As an aside, when my daughter built her house the windows that I spec'd had a U.17 (R 5.9), with a design pressure of 100psf, and air infiltration of .003cfm (that is not a typo, .003cfm is correct). They were not $199 specials, but they were very much cost comparable to any good window on the market.



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RE: Repair, Don't Replace, Old Wood Windows

Oberon,

Well, end the end, it looks as though we are in substantial agreement after all. I would probably lean more toward repair, you toward replacement, but this is just a matter of emphasis.

Enjoyed the conversation and look forward to the next one.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Surely this is the Best Windows Post Ever! Thanks so much to all of you for a civil, thoughtful, and illuminating discourse.

Lynn


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RE: Repair, Don't Replace, Old Wood Windows

So, in practical terms, how does someone (like me) go about determining whether old wood windows can/should be restored/upgraded, and if that is, indeed, the best option or not? Further, who in the world does one call for such a job? Window replacement companies are a dime a dozen. Restoring old wood windows? How do I find that guy?


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RE: Repair, Don't Replace, Old Wood Windows

Brickhouse_9:

The FBI wants to talk to you about the mysterious disappearance of Brickhouse_1 through Brickhouse_8, but back to the topic.

If you live in the North East, restorers are plentiful, and are probably in the yellow pages. If you live in an urban area elsewhere, ditto.

If you can't find one in the yellow pages, go to your local architectural salvage company. They will most likely know of someone who restores the old windows they sell and can be a source of technical information otherwise.

Best of luck,


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RE: Repair, Don't Replace, Old Wood Windows

I will caution Brickhouse 9 and others that it is important to get a bid upfront for such restoration, with a detailed description of exactly what will be done with each sash. I was a complete dope and found a nice enough, well-meaning, highly skilled fellow through the internet, to meticulously restore old doors and windows in our kitchen renovation for our 100-year-old house. He shall remain nameless, and I suspect that he lives somewhere "on the spectrum" (as in, on Mars) -- seemed to be completely lost in the fine points of window and door restoration and weatherproofing, to the point of losing touch with the reality of things like COST when compared to just popping in new high-quality triple-paned Whatevers. We were willing to pay a premium for high-quality restoration of solid old fir windows, but not a premium that was a multiple of the cost of high-quality new materials. Unfortunately he billed by time plus materials -- not a good arrangement for someone who approached the job as if it were the Sistene Chapel -- his initial bills for the back door and transome alone were staggering, and after paying him for his work-to-date I released him from the agony of any further work on our house. Back door looks great though! :)

Still trying to recycle our old windows, but it's not easy. I think I might have to retire from my own profession and take up antique window restoration....

Lynn


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RE: Repair, Don't Replace, Old Wood Windows

brickhouse, check out these two - you can get regional referrals from them if you're in a different area:

http://www.windowrestorationne.org/
On this site, Jade at Heartwood is a great contact.

http://www.historichomeworks.com/hhw/education/SaveMaineWindows.htm
John Leeke is the contact there.

I'm not affiliated with either of them.


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RE: Repair, Don't Replace, Old Wood Windows

I agree with farmgirlinky. Always get an estimate, always check with the BBB, always ask for references.

But also be careful what you ask for. If you tell the restorer you want you old windows to "look like new", that's what you will get, and it will cost you. Tell him/her you want them in "serviceable" condition.

We have restored museum quality doors and windows to like new, but it cost a lot -- especially the business of hunting up old lumber to fit the period. Anything can be taken to extremes, and it looks like that's what happened to farmgirlinky. We have several artisans in my town who given enough time and money, can restore just about anything. But this is more restoration that most old houses really need.

Use a little common sense as farmgirlinky suggests.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

I very much enjoyed this discussion, too. My home was built in 1954, so it has no historical significance, but I do like the old windows, every pane of which I reglazed about 10 years ago - and it did help! Also, I got to see that the windows are in good shape, not rot. I do not like the aluminum storms/combo screens, and they don't provide much. (They do help some; take then off in winter and wind blows in as if the window was open)

I'm looking to replace my two bathroom windows for a couple of reasons. However, I am reluctant to do the same with all the other house windows because they work - and I like the way they look. I'm going to look into ways to do something different with the storms, maybe add coatings to the panes. (DH, 16 light)

Thanks


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RE: Repair, Don't Replace, Old Wood Windows

Thanks so much for this thread and the interesting discussion. I am trying to understand how restoration costs a fraction of replacement because so far to us it seems cost prohibitive. I am in the DC area and agonizing over the windows in our 1932 Arthur Heaton colonial. The windows are in good shape but over the years have been painted shut and the 1970s storm windows are falling apart. The windows are beautiful, or once were, have chains in place, brass pulls. I got a quote on restoration, though, that with a full restoration, weather stripping, dip and repaint to remove lead paint and everything else to make the windows like they were when they were new will be about $1200 a window. And then, to add storms on top of that not only covers up the beautiful windows but adds to the cost and we just can't do it. We live near a busy street so sound insulation is as important to us as energy efficiency, perhaps more so.
I am considering only restoring the front windows, but seems like it would look odd elsewhere in the rooms with newer windows.
My inclination otherwise is to go with fiberglass, which look reasonable when compared to restoring + new storm windows. I don't know if I could get over the guilt though if we get rid of the original windows.
Any advice would be appreciated - does the cost of the restoration sound typical? We got a highly respected person who does many buildings much older than ours, so I wonder if we are getting more than we need.


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RE: Repair, Don't Replace, Old Wood Windows

threeunder5,

I have not seen your windows (but you can post a pic of the worst 3 so I can look at them), so I really can't say is the estimate is or is not reasonable. I used to live in DC (Univ of Md, 1971, BA, 1974 MA - Go Terps) so I know labor costs are out of this world.

Nonetheless, look at the cost of replacing your windows with new windows that closely match you originals (you are unlikely to find an exact match). Hardwood inside, similar hardware, etc -- and I'll bet the price is somewhat similar.

First, get creative. Restoring all of your old windows to like new may be cost prohibitive, but restoring them to serviceability may be less costly. Do your second story windows need to be stripped? Dip stripping is for windows with historical significance. Maybe they can just be painted over -- who can tell without a ladder. Does all the glass need to be replaced? I'll bet not. Sounds like your asking for a Cadillac job on a Chevy budget.

I cannot discuss what my company can do on this forum, because it violates forum rules to advertise or solicit business, but contact me to discuss options.


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RE: Repair, Don't Replace, Old Wood Windows

I will tell you the last thing you need in my opinion is a "window consultant" who spam's websites


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RE: Repair, Don't Replace, Old Wood Windows

Here are some shots of a few windows - not the best shots.
The windows themselves look pretty good - they just don't function (the storms look horrible in comparison).
Thanks for your suggestions and ideas!

Here is a link that might be useful: photos of windows


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RE: Repair, Don't Replace, Old Wood Windows

threeunder5,

I can't see why these windows need a full restoration if the primary problem is that they just don't work.

A complete weatherstripping, sash weight replacement and insulation should be less than $250 per window even in your area. Figure a bit more for 2nd story windows. Even if the ballasts are spring ballasts, which are more expensive and a nuisance to fine tune, $300 should be the max. I would certainly get some other estimates.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Thanks so much xoldtimecarpenter.
We were interested in stripping the paint because of the significant lead readings when we had it tested, and our small children, but perhaps we only need to do it in their rooms. I emailed you directly the list of what the proposal included doing. I suppose I should also be concerned about their energy efficiency, but we haven't lived here in the winter yet so I have no idea if they let in the cold or not.


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RE: Repair, Don't Replace, Old Wood Windows

If your house was built before 1978 you have lead on or in every surface of your house: walls, floors, ceiling, moldings and mill-work, cabinets, doors and windows, heat registers, and the concrete floor of your basement. You cannot possible get away from it. Unless you are going to remove all of the paint and varnish in your home down to bare wood and plaster and start over, you are going to have lead in your house.

Let's not let the current lead scare get out of hand like the phony "toxic" mold scare. Lead paint cannot hurt you unless you can somehow ingest it. And you have to ingest a lot of it before it does any serious harm.

Your children cannot ingest lead by rubbing against a lead-containing paint. They can ingest lead paint in just two ways: The can breath in small particles of paint floating in the air and they can eat it. Of the two, eating it is far more likely to cause harm. Why? Because lead is heavy and if it is in the air, it is not likely to stay in the air for very long. Once it hits the floor, you vacuum it up like any other dust and it gets trapped in your HEPA filter. So, if your house is not being renovated using processes the put lots of dust in the air, lead in the air is not a problem. (If your house is being renovated, the renovator should be following EPA-RRP rules, and dust in the air should still not a problem.)

If children eat paint, it is likely to be off the door molding (we call it the "casing" in the trade) or window sill (which we actually call a "stool" -- the "sill" is outside). The real solution to this problem is to firmly discourage your children from eating the woodwork. Whether or not it contains lead paint, it's just not very good for them, and it leaves ugly marks on the wood.

Stripping your window to avoid lead problems is a ten dollar cure for a twenty-two cent problem. But if you are really worried about it, strip and repaint just the sill, and leave the rest of the window alone. Stripping the rest of the window is a total waste of money. And, I would actually hold off on any stripping of any kind until I saw actual tooth marks on the window sill that cannot be reasonably attributed to the dog. (Your dog is not at risk. By the time the dog ingests enough lead to do harm, he or she will be long dead of old age.)

As to energy efficiency. I can almost guarantee that windows that old are not particularly efficient. But if you have not lived through a winter, it is premature to think about restoring or replacing the windows. You don't know if you have a real problem yet. Wait 'til Spring, then make up your mind. While old windows may not be as energy efficient as new thermal replacement windows, they are acceptably efficient to many people so long as they do not leak a lot of air. See if that is a problem before restoring your windows. You may be anticipating a problem that does not really exist.

Take the money that you were going to use to restore the windows and do something really energy-saving like buy a new high-efficiency heat pump, water heater or nice, new hybrid car.

I did read and respond to your e-mail. I would not have anyone do that much work to my windows unless I happened to live in the White House (Maybe not even then. It's just another government building, after all.) Most of it is just not necessary. This guy must have some very rich customers. I wonder how I can get into that market?

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

I'm a little late on this thread, but have appreciated the wisdom so much. Thanks to all of you.
I am trying to decide whether to replace or repair some or all of my windows and doors. The house is an all brick traditional in a fairly upscale subdivision. It was built in the 80's and has double-hung, double paned, wood windows. There is no brand that I can see, and they seem to be original, though I am not positive about that.
Two windows have one of the two panes broken. A few have lost whatever keeps them from closing. And a few are a bit foggy. All the wood is in fine condition.
I am not at all excited about the idea of putting vinyl windows in where wood has been, yet it seems to be "the norm". In fact, I'm not at all excited about replacing windows that really have life left in them.
Of course all the sales pitches want me to think I'll save a fortune in heating/cooling bills. (I'm in East TN, so we get 100F in the summer and negatives in the winter.)
The doors are a bigger concern for me. I can see daylight in one corner of the front door. I'm thinking if I replace just the door, that won't fix that problem. Is it normal to replace the whole frame and all? There are "sidelights" on the doors- do those get replaced with the windows or separately?
The back door has lots of cold air coming in when it's cold. It seems that even though I have lots of weather stripping in place, it doesn't close tightly. Again, I'm thinking that replacing just the door won't help.
I'd be glad to post pics and so appreciate all input.
THANK YOU in advance-
Tami in TN


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RE: Repair, Don't Replace, Old Wood Windows

"If your house was built before 1978 you have lead on or in every surface of your house: walls, floors, ceiling, moldings and mill-work, cabinets, doors and windows, heat registers, and the concrete floor of your basement. "

Not correct.

Lead paint uses lead acetate as a gloss improver and hardener.

Lead oxide pigments disappeared a LONG time ago to be replaced with titanium oxide.

The EPA has been greatly exaggerating the amount of lead paint for a long time.

It was also expensive paint, and not used in many homes at all.


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RE: Repair, Don't Replace, Old Wood Windows

I agree brickeyee. We test house frequently for lead paint. For someone to claim that if your house was built before 1978 that you have lead paint is ridiculous. I recently tested a house built in 1951 and it did not have lead paint. I have tested others that were built in the early 1960's that did.

Paint manufacurers started phasing lead out of paint in the 1940's and by the 1960's very few of them were still making lead-based paint for residential use. When the law finally banning lead went into effect in 1978, lead paint had not been used residentially for a long time.

The new EPA lead paint rules are nothing but a money grab from contractors. Why is it OK for a homeowner to use a belt sander on a windy day, to sand the exterior of a home built in 1920, spreading lead paint dust all over the neighborhood and not OK for a contractor to simply remove an old window without having to implement EPA containment procedures?


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RE: Repair, Don't Replace, Old Wood Windows

Our home was built in 1969 and our wood windows appear to be in fine shape other than peeling paint. I am intersted in having them restored to ensure they last as long as possible. Any sugeestions for finding someone to do this for us in Northern Virginia?


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RE: Repair, Don't Replace, Old Wood Windows

Email brickeyee


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RE: Repair, Don't Replace, Old Wood Windows

I both agree and disagree with brickeyee and skydawggy.

True, paint manufacturers began phasing out lead in paints in the 1950's (some, but only a very few in the 1940's). But into the early 1970's a lot of paint still contained lead. And, paint is not the only source of lead. Most primers still contained lead as late as the 1970s, and so did most varnishes prior to polyurethane. Radiator paint is very likely to contain lead, as is the factory applied paint on old style registers.

So tell the whole story, guys. Some houses will test lead free. But most will not. And, I have basic doubts about the testing procedures used. Everyone tests wall paint and mouldings, but I have never seen anyone, except us, test floors, stair treads, radiators, register covers, painted cabinets, etc. Test all these things, and you will probably find lead in a pre-1978 house.

I do agree, however, that the current EPA-RRP regulations are a joke. They are much more expensive to follow than the EPA suggests. In fact, there is now ample evidence that the EPA simply lied about the expected cost -- and there is a class action lawsuit pending on just that issue. Further, the current regulations are unlikely to be very effective in containing lead. They are a ton of cure for an ounce of problem, and they are unlikely to reduce the problem by more than a gram.

Still, it's the law at the moment, and, as bad as it is, the best solution we have right now for containing a dangerous substance that is very difficult to contain.

As for contractor costs -- almost all the financial cost is passed on to the homeowner. My cost is that the regulations are tedius, annoying, burdensome, and unlikely to be effective -- which irks me no end.


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RE: Repair, Don't Replace, Old Wood Windows

EPA regulations do one thing successfully...create waste.

Waste can be many things but it is certainly wasting the following: resources, plastic, time, money, and customer expense.

Most home built between 1950 and 1978 will test lead free from a window impact side of things and that is who the EPA is targeting. Do you see them levying fines against renovators that are in there busting up plaster and lathe...nope. No money in it.

The truth about lead is that a contractor (from the window end of thing) will be hard pressed to generate a lead hazard for a home or a small child. Most of the elevate BLL (Blood Lead Levels) that I have tested and seen in my previous employment, where this information was collected and tested for, were in home with deteriorating finishes (i.e. flaking paint) that small children consumed and or had long term contact with (hands and feet of a crawling baby for example).

If a contractor (speaking of window again) does a good job of cleaning up his project site after install, the exposure is next to nill.

Insert replacements do not generate any dust in the process and there is invariably more exposure from the windows operating up and down against the stops than there every is during the removal and preparation of that opening.


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RE: Repair, Don't Replace, Old Wood Windows

+1

EPA laws make more trash than they clean up most times.


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RE: Repair, Don't Replace, Old Wood Windows

The lead contamination lawsuits against paint manufacturers has already started. They are making arguments similar to those made against tobacco companies. It's all a big money grab.


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RE:: Repair, Don't Replace, Old Wood Windows

xoldtimecarpenter,

Broad sweeping statements like yours are not helpful as they are too encompassing. The likelyhood of lead paint existing has less to do with the age of the house than it does with who the builder was. That's why we have tested numerous houses in a subdivision built in the late 1960's and found lead paint in every one of them and also tested subdivisions built in the 1940's and found no lead paint. It also depends on the location of the house. Homes in the Northeastern U.S are more likely to contain lead paint on a whole than those built in other areas of the country. Even the EPA acknowledges this.


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RE: Repair, Don't Replace, Old Wood Windows

Hi-

I'm trying to determine if we should repair or replace a wood, double hung window with broken spring mechanism and in need of re-glazing. If we lived in a cold climate, the answer would be more clear. However, we live in Sacramento, CA where I think cooling is a bigger deal than heating.

How do the old double hung wood windows do in hot areas (since the posts said that radiation plays a more predominate role)? Are they still relatively comparable to double pane?

Thanks for any advise!

Lamaia


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RE: Repair, Don't Replace, Old Wood Windows

Comparable in what way? If you are refering to the windows ability to reflect damaging UV radiation, newer double pane glass will reflect as much as 99%. If you are asking about solar gain from radiation, double pane with certain LoE applications will block more than 3 times the amount that single pane glass blocks.


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RE: Repair, Don't Replace, Old Wood Windows

"Email brickeyee"

Not taking on any new projects.


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RE: Repair, Don't Replace, Old Wood Windows

In a warm climate, the energy savings of repalcement vs. repairs would be even less since your overall energy bills will be comparatively smaller. Plus the temperature difference is smaller. You lose more heat when it's 10F outside and 70F inside, than even if your in Pheonix and it's 110F outside and 75F inside. That only 35F difference, vs. 60F in the first comparison.


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Real world observations

OVerall, great article with excellent references.

We recently purchased a 1925 3200sqft 2 story home with original windows. All 42 of them. Replacing them would likely cost upwards of $25k. OUr electric bill for the 1st half of July was only $120 and it's maintaining humidty level extremely well. 48F indoor dewpoints with 72F dewpoint outside. I think the old windows are sealed very well.

We repainted the exterior of all the windows (had peeling paint) and we plan on adding storm windows over the next 3 years. Probably do a dozen at a time, each year.

I think for the front windows we might take a different approach and do sash replacements or have them rebuilt with upgraded glass. There's also 3 or 4 other windows that need attention and have their sash cords replaced.

The argument by the windows companies would have you think that my heating and cooling bills must be $800/month. The fact that they aren't proves that old windows perform much better than they want you to believe.

Even if my heating and cooling bills went to $0, I'm still looking at a 10-12 year payback. Factor in the "Cost of money" and you're at 15 years.... and guess what, they will likely start leaking and need replacing in 5-10 years after that.

Our previous 1968 home, we replaced 10 windows. They had functional issues and looked ugly, so there were other factors. But just looking at actual energy savings, the payback would have been 25-30 years. Based on their quality and how quickly they were "degrading" we would need to replace them within 20 years.


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RE: Repair, Don't Replace, Old Wood Windows

I've enjoyed this post and conversation (the non-technical parts!). We live in a 1926 bungalow in St. Paul and are thinking of replacing windows but I hate to lose the wood windows. In Minnesota, we have to have storm windows and insect screens, so twice a year we have to do the big switch, which is a hassle and the storms/screens are getting old and some need repair. A bigger hassle is washing the windows, which is virtually impossible on several because of their location. I have questions for xoldtimecarpenter or others who are experts on restoring wood windows. Is there a restoration of old windows that would mean the end to switching storms and screens? I.e., can a double pane be put on an old window and screens left up year-round? And is it possible to convert old wood windows to tilt-in windows? I'm having difficulty imagining how old windows could be restored and have easier upkeep for people with some increasing challenges. Thanks for further info.


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RE: Repair, Don't Replace, Old Wood Windows

Motoguy,

You are ASSUMING heating and cooling costs will not increase. You are in for a big shock in the coming years. What do you think an automobile that get 6 mpg is worth these days?


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RE: Repair, Don't Replace, Old Wood Windows

None of the respectable pros on here that I know of will claim that windows are the weak link in your home (in a majority of the homes out there, however, there are some homes where windows are the weak link) when it comes to energy.

That not withstanding, windows are certainly a part of the building system from both an insulation and envelope component and can have significant impact on home performance depending on the nature of the malfunction.

Replacement is not the magic bullet and especially if the work is not a competent professional.

Restoration and retrofitting of older, historic windows are certainly options and worthwhile considerations if the windows are of value.

Putting storms on an existing window is not the magic bullet either and many homeowners don't want to mess with them.

Find out what is right for you and your equation, but be sure to have the facts in front of you before you make a decision.


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RE: Repair, Don't Replace, Old Wood Windows

I read your article about not replacing old wood windows. We have beautiful wood windows from the 60's that we are close to replacing. What type of person do I hire to weatherize the old windows. We were thinking of just replacing the combination storm window. Is this just a waste of money?


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RE: Repair, Don't Replace, Old Wood Windows

SurlyStreet,

The answer to your question:

"Is there a restoration of old windows that would mean the end to switching storms and screens?",

is "of course". They are called combination storm/screen windows and they are available everywhere for about $65 each, plus installation.

For WindowsOnWashington: "None of the respectable pros on here that I know of will claim that windows are the weak link in your home" Really? Most dual glazed windows max out at R-3, whereas a reasonably insulated wall is R-13. Windows are a HUGE hole in your insulation -- certainly the weak point in any well insulated building envelope. I don't think any "respectable pro" will deny this obvious fact.

Regards,


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Replace Combination Windows

Loreethegardener

If your windows need repair, it probably would not do much good just to replace your combinations -- assuming that they even need replacement.

I don't know where you live, but look in the usual places for window restorers, yellow pages, etc.


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RE: Repair, Don't Replace, Old Wood Windows

xoldtime,

I was speaking to the fact that windows are not the magic bullet that they are claimed to be by most window suppliers. You certainly agree with this.

Windows certainly are the weak link in a wall assembly although your claimed R-13 is not accurate as long as we are being factual. I was speaking the the idea of windows being the weak link in the home in total.

FYI, plenty of double glazed windows are very near the R-5 number and there are plenty of triple glazed windows that are over R-7. An actual 2x4 frame wall is going to be much closer to R-7 to R-9 when you figure in the thermal bridging of the studs and the actual R-Value of fiberglass vs. the claimed value.

I think you missed my point. I was supporting the idea of restoration of windows if the homeowner wants to stay with the look of their existing windows or has a historic home. In those applications, the retrofit of an existing wood window and the application of an insulated storm are certainly suitable options.

Windows are part of the building systems but if we are talking about dollar for dollar ROI timetables, I can spend money on a myriad of other items that will be much more aggressive. That was my point.

To that extent...aren't we pretty much agreeing?

I was certainly including you in the list of people that I consider to be respectable, although, we disagree on most of your math when it comes to the support of your restoration vs. replacement argument.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

Sorry. Obviously I misunderstood what you were saying.

However, I don't think my math is wrong. If I use the stated R-value of a window, then I use the state R-value of wall insulation. The static test used to evaluate thermal resistance of window assemblies is very flawed, and greatly overstates the actual R-value. I doubt a window with a stated R-value of 2.5 actually performs much better than R-1.2 in actual use. According to the ORNL whole wall study, wall R-values are also greatly overstated. Fiberglass in a stud wall has a whole wall insulation value of 42% less than its stated value, due in part, as you noted, to thermal shorts, but also due to poor installation. A stated R-value of 13 in a wall means the wall is probably performing at R-7.5 or less.

Yes, there are indeed thermal windows that rate very well, on to the NFRC static test, up to R-11 for some superior triple glazed products. But how many of these windows are actually installed? I'll will bet that well over 90% of replacement windows have a stated R-value of R-2.5 or less, and an actual performance of less than R-1.5.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Well, if you are going to invalidate any test results that run contrary to your contention then it's possible to prove the moon is made out of green cheese.


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RE: Repair, Don't Replace, Old Wood Windows

xoldtime,

We will have to agree to disagree again.

Most of the issues that plague insulation performance in a wall assembly are not possible in well designed windows.

i.e. improper alignment, convective air movement, over compression, etc.

If a window is installed properly, the performance does not change at all as compared to its measured R-value. Most good double pane windows are near or above an R-4 and that is exactly how they will perform.

A properly installed window, that is airtight, will function exactly at its stated value.

Claiming that a wall is R-13 is incorrect from the outset because even if it is installed perfectly, it will never approach that number. Perfectly aligned fiberglass will still never approach that number and will degrade over time (settling, movement, crack development and air movement). A window will not.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

Even the NFRC admits that its testing protocols do not account for transfer of heat by convection, because convention effects are deliberately engineered our of the testing process.

Convection, however, is one of and probably the most important of the primary means by which heat is transferred out of the building envelope. A rating system that ignores convection effects cannot possibly be even remotely accurate.

All U-value ratings tell you is that window A, with a higher rating, will probably perform better than window B with a lower rating -- but the rating system is ordinal. It can be used for comparison, but not for determining actual heat transfer resistance.

Field tests of the actual performance of windows installed in houses suggest that their actual performance is far below their rated R-value.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

xoldtime,

Please re-read Oberon's post in the middle of this thread.

Convection is not the primary means of energy movement through an insulated window, radiant is. Conduction is second to that and Convection is 3rd.

This is very apparent in the pictures that you cite in your own posts.

Quoting my own post here....

Even if we assume that convection is the dominate pathway for energy to leave or enter the structure (which is definitely debatable if not out right false depending on the climate region) what do you think drive convection?.... Differential temperatures is what drives convection. Differential temperatures are mitigated by limiting conduction and radiant losses. By your math, insulating walls is an over-hyped building approach if convection is the culprit.

If I am in Texas and standing in front of a window, is that convection I am feeling?


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RE: Repair, Don't Replace, Old Wood Windows

Do they use convection or infrared ovens when they bake green cheese?


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

Conduction is the primary method of heat movement through glass. Convection is the primary method of heat movement to and through the window as a whole.

If you are standing in front of a Window in Texas, then you are probably feeling radiation -- maybe from the sun, or maybe from Los Alamos. I'd move away from the window.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Sorry, you are incorrect again xoldtime.

Radiation is the primary energy flow through a window. Seeing as most windows are 80% glass, I think it is safe to say that what is the primary source for energy movement through the glass is what is most representative of the window as a whole.

Radiation is responsible for about 2/3rds of the heat loss through a window. Conduction is next and Convection is last.

These are not really debatable points but more specifically identified and accepted facts.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

In a net heating climate, radiation plays a minuscule part in heat transfer through a window. Before I would even entertain the notion that radiation is the primary means of heat transfer through a window, I would have to see a citation to a non-window-industry study establishing the same.

Radiation is the transfer of heat by means of electromagnetic waves. All objects radiate energy in the form of electromagnetic waves. The rate at which this energy is released is proportional to the Kelvin temperature (T) raised to the fourth power, usually expressed as R = kT4.

The hotter and denser an object is, the more it radiates. The sun radiates quite a lot. But the object holding most of the heat is a house is air. House air is, as one might suspect, at room temperature. At this temperature there is very little radiation emitted and any heat loss through radiation is far outpaced by loss through convection and conduction.

In the NFRC-sanctioned heat transfer test, a calibrated hot box is used to measure U-values under still and non-convective air conditions. It is not possible using this test to separate heat transfer methods, just over all heat transfer. But studies that do separate out heat transfer methods are pretty uniform in their conclusion that convection and conduction are the important heat carriers in net-heating areas of the country.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

OTC,

I would really like to know where your information is coming from, because with all due respect, it is sinply wrong.

Radiant accounts for 60% (slight variation possible depending on enviromental conditions), which is hardly miniscule. Conduction accounts for the remaining 40%.

To say that radiant is not a factor is to completely disregard the reason why LowE coatings exist and why they work. LowE coatings restrict the transfer of radiant heat thru the glass - and they work exactly as advertised.

Window R-value information that you were suggesting earlier is at odds with literally miliions of dollars of both lab research and development as well as field testing. Yep, there is a good bit of field performance testing going on as well to verify the published information. No one is engineering testing to achieve specific (false) performance numbers. It ain't happening.

Have a great evening...


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RE: Repair, Don't Replace, Old Wood Windows

I will renew my point that if convection is the dominant pathway, insulated walls are totally unnecessary. Obviously that is not the case.

Once an inside piece of glass is warm, the pathway that the energy is traveling to the outside pane is most dominantly radiation. Keeping that pane from warming and the energy flow from moving to outside is primarily what Low-e does.

The inside conditions of an insulated glass window do not change in a dynamic vs. laboratory environment which was a large part of your accusation of the NFRC test.

There is certainly some convection happening inside the sealed glass unit (hence the reason that argon filled IGUs show a marginal improvement in total R-value as compared to air filled).


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington
Oberon


Guys, next time you are going to a show or convention in the Midwest, let me know. You guys definitely add a little sparkle to my existence.

Let's start with this: Oberon is not wholly wrong, and if we all lived in hotboxes, he would be absolutely right. Unfortunately, we do not live in hotboxes, we live in houses. And for houses, he is wrong.

Almost all of the data on heat transfer through windows, and certainly the results that Oberon reports is based on hotbox tests.

For those who do not know, hotboxes are the devices used to test window heat transfer resistance in windows. They are a completely artificial environment created solely for the purpose of testing windows. The construction of the hot box and the testing procedure is defined by a window-industry group, the National Fenestration Research Council (NFRC).



Here is a typical example of a NFRC window testing hotbox. Note that the heat source for this hotbox is radiation from heat lamps.

Hotboxes used in NFRC tests almost always use some sort of radiant heat source because it is the most precisely controllable heat source. Naturally, in the hotbox environment most heat transfer is going to be by radiation, since the heat source emits copious radiation.

Hotboxes are designed to eliminate a great many environmental factors to help ensure that testing is standardized. The most important factor eliminated is air convection on the hot side of the hotbox, and air movement (atmospheric convection) on the cold side. Unfortunately, eliminating these environmental conditions makes the hotbox useless in predicting performance in the real world where there is substantial convection inside the heated house, and cold air movement outside the house. Convection is what moves heat in the real world.

Window Performance in a Hot Box

Let's see what happens in an artificial hotbox environment when a dual pane window is subject to heat from a radiant heat source:

The Integrated Glass Unit (IGU) that forms the dual-pane is composed of two sheets of glass and air (or an air substitute. like Argon -- we will get to these in a minute).

Opaque materials absorb radiation, but transparent materials like glass and air let it pass right through. Both glass and air are transparent, so most of the radiant heat energy goes right through. As a result, in the artificial hotbox environment, as Oberon suggests, about 60% or so of the heat energy is transferred through the windows by radiation.

But the glass (or more accurately the minute impurities in the glass) absorb some of the radiant energy. This warms up the glass surface facing the source of the radiation. Glass is a pretty good conductor of heat. At 0 degrees centigrade (0C), window glass has a Heat Transfer Coefficient (HTC) of .96. By comparison, air is .024 and expanded polystyrene (a common insulation material) .03. The higher the HTC, the more conductive a material is. It does not take long for the heat absorbed by the glass to transfer throughout the glass pane by conduction.

Now the heat has reached the air between the panes of glass in the IGU. (We will call this the interstitial air in contrast to the room air on the hot side of the window and the outside air on the cold side of the window.)

The interstitial air is now receiving heat from radiation, directly from the hotboxs radiant heat source, and from the surface of the glass pane warmed up by conduction.

Still air is a pretty good insulator. It has an HTC or .24, better than a lot of insulation materials. Unfortunately air is never still. It is always moving.

Interstitial air is not an exception. It is now sandwiched between the warm inner pane of glass, and the cold outer pane. Air touching the cold outer pane gives off a little heat and becomes, as a result, a little denser. Cold, dense air falls. The air touching the warm inner pane of glass absorbs a little heat, getting a little less dense, and it starts to rise. Very quickly a circulation current forms. This current draws heat from the warm inner pane and conveys it to the cold outer pane. If the heat difference between the inside pane and the outside pane is large, the convection current moves faster, conveying more heat. If the difference is slight, it moves slower, but it never completely stops moving.

This is the process of convection.

So now we have two means by which the interstitial air is heated. It absorbs some heat from radiation emitted by the radiant heat source, and some from the warm inner pane, which starts a convection current that transfers the airs heat to the cold outer pane. There is also a third source. The warm inner glass has become a radiating surface, although the amount of radiation it produces is very tiny. Still it contributes some heat to the interstitial air.

The only barrier left to the heat getting outside is now the outer pane of glass. Since it is good conductor of heat, and radiation passes right through it. Its contribution to the insulation value of the window unit is negligible. Its major purpose is merely to contain the interstitial air.

So we can fairly conclude that in the artificial hotbox environment, radiation is a major factor in heat transfer. Convection on the room air side, and on the outside of the test window is virtually eliminated by the artificial test environment, so it plays virtually no part in heat transfer. There is still some convection in the interstitial air, and it accounts for some of the remaining heat transfer, but most of the remainder is through conduction through the glass and framing members.

That radiation and conduction play such a large part in heat transfer in the hotbox environment is an expected result of convection being almost entirely limited from hotbox testing. But what if convection is restored to the environment?

Window Performance in the Real World

I have installed thousands of windows in houses, apartments, businesses, industrial plants even in one war monument, but I have never installed a window in a hotbox.

Why is that, you ask? Well, its because people dont live and work in hotboxes, they live and work in buildings. Consequently how windows perform in buildings is much more important than how they perform in artificial testing environments like the NFRC hotbox.

In houses, there is no radiant heat source directly behind the windows to produce radiant heat. There is just warm air. Radiation is, of course, present in anything warmer than the environment around it, but it is the dense materials like metals and concrete that produce significant radiation when warmed, not gases. Air produces such an insignificant amount of radiant heat that its radiant effect is usually completely discounted in laboratory tests.

As far as heat is concerned, your window is just a weak spot in your wall's insulation, and like water, heat seeks the path of least resistance out of any container. Most heat gets out through the windows. This is due to a natural physical process by which windows tend to draw heated room air to themselves. This process is room air convection. Air transfers most if its heat by convection.



This diagram shows a vastly simplified room air convection process. Actual room air convection may involve hundreds, even thousands, of air currents, big and small, all tending to move heated room air toward the windows.

Convection is a natural physical process that occurs in any room that contains air. Heated air rises, cold air falls. As heated air comes in contact with the room's windows, the air gives up some of its heat to the colder window glass. Now cooler and, therefore, denser, it starts to fall. As it falls, still pressed against the glass, it gives up yet more heat, getting ever colder and denser, and falling even faster. This creates a vacuum which other warm room air rushes to fill. This new air is in turn cooled and also falls, continuing the cycle.

Until someone figures out how to repeal the physical laws of thermodynamics, it is completely unstoppable.

Room air convection would not have much consequence if just the little bit of air directly in front of the window was the only air affected. But the vacuum formed by the falling cooled air draws heated air not just from above, but from both sides of the window, forming convection currents that very quickly reach to every corner of the room, directing almost all the room's warm air to the window through one convection current or another.

So, in the real world, heat does not get to the window from a convenient radiant source placed behind the window, but by air convection. There is no radiant source. No radiant source, no radiation. No radiation Well, without radiation it is impossible for 60% of the windows heat loss to be through radiation. Thats pretty obvious to anyone.

The heat from the warm air is conducted through the inner pane by conduction. But when it hits the interstitial air, most of the transfer is again through convection, as described above. Finally, the outer pane conveys the heat to the outside world through conduction. But the most important heat transfer method in the real world is convection. Without it heat would not get to the window as efficiently, and would not be transferred from the inner to out panes as readily.

Window manufacturers recognize the importance of slowing convection, and do what they can to limit its effect.. Unfortunately, there is not a lot they can do. What they try to do is to replace the air between the glass panes with a heavier gas such as Argon or Krypton.

Heavy gases are more viscous and flow more slowly, thus slowing down convection. These gases can temporarily raise a window's resistance to heat movement considerably. Unfortunately they are not permanent. They leak out over time, and every manufacturer that uses them admits that they leak. No one warranties in-fill gases against leakage. After 10 years they are all but gone and have been replaced by, you got it, plain ol' air. So that extra $5,000 you spent for a house full of Argon- or Krypton-filled windows just went adios; and the environment got a nice dose of Krypton or Argon that it did not really need.

I think temporary measures such as films that degrade and gases that leak should not be allowed in determining a window's thermal resistance. Of course, I do not have a lobbyist in Washington, and the window industry does, so my opinion is unlikely to prevail. But I do strongly suggest that anyone contemplating buying a gas-filled window should pay attention only to the R-value (or U-Factor) rating without the gas. In a few short years they will be gasless -- and there is no way to get a gas refill.

How to Test Windows

The problem with the NFRC testing procedure is that the rigidly controlled, virtually airless, artificial environment is not a very realistic simulation of the real world environment windows actually inhabit. It tests only two of the three heat transfer methods: conduction and radiation. It virtually ignores convection. But convection is how most heat loss occurs in the real world.

The consequence is that the tests results dont tell us much about how well a window performs in the real world. They tells us only how well it performs in the test.

And, unfortunately, heavy reliance on tests results performed in an artificial environment tempts window manufacturers to make windows that perform well in the tests, but not necessarily in the real world. Most potential window customers know little about windows, but do know that a high R-value is better than a low R-value, so to sell windows, window makers strive for as high an R-value rating as possible in hotbox tests, so they can print the high value on their window labels and thus sell more windows.

A case in point are low emissivity films. These are (usually) metallic coatings applied to window glass that help block radiation. In hotbox tests, these are important to securing a high R-value (or low U-factor, since window manufacturers insist on using the much less well-understood U-factor. For more information see R-value, U-value... What Do They Mean?). In the real world, not so much. Radiation is not a significant factor in heat loss through windows in net heating climates. In climates where the summers are fierce, the films are useful in blocking direct solar radiation in the summer, but awnings and shades are more effective -- and usually a lot cheaper.

The only proper way to test windows for resistance to heat transfer, and get meaningful results, is to duplicate the real world as closely as possible. This requires a testing environment as much like a building as possible. The ORNL studies of wall insulation used just such a realistic environment, and produced meaningful results. The NFRC can do the same thing.

First, build an insulated box inside an insulated box. Provide a forced air heating source for the inner box and a cooling apparatus for the outer box. The inner box simulated a room in a house, the outer box the great outdoors.

Next, test how much heat had to be added to the inner box to maintain a temperature of 70 degrees for 24 hours when the outer box is a constant 30 degrees. This is the baseline heat consumption of the test room

The, add a window, properly install in the inner box. Test how much heat has to be added to the box to maintain a temperature of 70 degrees for 24 hours in the same 30 degree outside environment. The additional heat above the baseline amount is the net heating cost of the window. This can be expressed in BTUs per hour (BTU/hr) which is how a great many heating measures are expressed.

The window that requires less additional heat is the more efficient window. It could not be simpler or more common-sensible. Hell, even a caveman could do it.

But no one has done it, at least not directly.

What they have done, and its almost as good, is to compare the heating requirements of a house before and after thermal windows are installed. The heat use in the house is measured before and after replacement windows are installed to see what difference replacement windows made. Of course it is harder to control variables in a real world environment. So the more effective test is to measure heat use for several years before and several years after the improvement so that random environmental factors can cancel themselves out.

The results of these tests have uniformly not been good for the window industry, so not very many window mavens talk about them.

In most cases the difference in heat consumption was negligible. Which suggests that the hotbox tests greatly exaggerate the thermal efficiency of the windows they test.

As for WindowsOnWashingtons statement that if convection is the dominant pathway, insulated walls are totally unnecessary, I will only say that convection is the dominate pathway by which heat escapes through walls. And insulated walls are necessary to slow the convection process. I wont go into details here, but take a look at Insulating this Old House.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Good morning,

I am wondering if anyone is reading all this anymore, other than the three of us? Personally, I am enjoying it and I think its been a lot of fun...I have a sneaking suspicion that it takes something of a nerd to go all the way to this point. But having said that...here goes:

OTC, you have made some good logical arguments using layman's logic, but your arguments show a lack of in depth knowledge about glass/window industry testing and performance.
For example, you mention the hot box test even to the point of posting a picture of one, but if I were to ask what percentage of IGU's (and btw it's Insulating Glass Unit, not Integrated) are subjected to that particular test and why, what would you answer?

At its very simplest, physical testing is used to accomplish one of three things.

First - when the performance characteristics of a particular material or combination of materials are unknown and the testing is required to establish baseline performance criteria.

Second - when the performance characteristics of the material(s) are known but they are being subjected to exceptional conditions that result in unpredictable results.

Third - when the performance characteristics of material(s) are very well known and the physical testing is used to confirm the results of predicted performance. Often in this last case physical testing is performed in order to confirm the result of extrapolated predictions.

In the case of glass and windows, the performance characteristics are exceptionally well known and are totally predictable. In fact, when someone goes to the NFRC website to look up the performance characteristics of a particular window, they are looking at computer-predicted performance criteria. They are not looking at physical test results.

On the other hand if someone went to Miami-Dade County website to research buying a window or door that is suitable for installation in a particular wind zone area, then they would be looking at products that were physically tested in order to be certified because of unpredictable results.

You also suggested that the hotbox was an "artificial" environment - and I would absolutely agree that it is but are you saying that a home or other building is not "artificial"? I would suggest that both are artificial.

If window performance is determined solely on the hot box test, which you suggested artificially enhances radiant heat performance, then why does the glass/window industry use both SHGC and U-value to evaluate window performance?

As a quick aside, I assume that when you stated in your post that a "vacuum is formed" when cooler air falls and then that vacuum is then filled with warmer air that you meant that as an illustrating analogy rather than suggesting that is what is actually happening?

You are absolutely correct that windows contribute to convection currents in a home. That is simple physics and that has been a known fact at least as far back as the introduction of both heat and windows in a building. There is a reason why the big old steam radiators (hmmmm radiator, interesting name for the heat source) were placed under windows.

You mention that the warm air loses heat as it passes over the colder window, so what happens to the heat that is lost when the warmer room air passes over the colder window?

Answer (which I know that you already know), it's absorbed by the glass. Is that convection loss? Nope, it's conductive loss.

The heat that is stolen from room air by the cooler glass makes the inner lite warmer - which increases convection inside the IG airspace - which results in warmer air against the outer pane of glass and conduction (not convection) loss thru the glass to the outside of the home. Does convection contribute to the loss? Of course. Is the loss mechanism convection or conduction? It is conduction. And when the outer pane of glass loses heat? It is primarily radiant loss. The heat radiates from the glass.

If you have a given square foot window, using a given number of lites, using a given LowE coating (or none at all), a given spacer system, and a given airspace width, then convection currents within the airspace and inside the home (given inside and outside temperatures; including wind and window orientation too btw) is totally predictable. There are no surprises. This stuff is well known and easily accessed by people who use it every day.

You stated in your last post: "So, in the real world, heat does not get to the window from a convenient radiant source placed behind the window, but by air convection. There is no radiant source. No radiant source, no radiation. No radiation Well, without radiation it is impossible for 60% of the windows heat loss to be through radiation. Thats pretty obvious to anyone."

Radiant heat loss and heat gain is very much a part of the real world. Your statement does suggest a lack of understanding of the nature of radiant heat energy. All objects above absolute zero emit radiant heat in the right circumstances. From inside a building to outside a building in winter is a perfect environment for emitting radiant heat energy.

Nature hates things not in balance, nature wants balance so that nature is going to do its very best to make sure that you have balance. There are three ways nature is going to affect that balance:

Conduction - heat transfer by means of molecular agitation within a material without any motion of the material as a whole.

Convection - heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.

Radiation - heat transfer by the emission of electromagnetic waves that carry energy away from the emitting object.

There are high solar gain coatings that pass direct solar heat and low solar gain coatings that block it. Solar heat is near infrared the infrared that bumps up against visible light spectrum (and as an aside, at the far end of infrared you get microwaves thus the infrared/microwave ovens).

Both high solar gain and low solar gain coatings block far infrared which is "cooler" infrared heat and includes any heat source including reflected solar, radiators (interesting term they use), TV set, stove, oven, refrigerator, electric lites, the dog and kids, any source of heat emits radiant energy period.

When dealing with windows you have a material (glass) that is transparent to the electromagnetic waves of the emitting objects in the home translated to whatever heat is in the home, no matter the source.

In the winter a home is a heat sink. That heat wants to go outside. Open a door or window and you create a massive convection current that lets warm air out and cold air in. But close the door or window and you have blocked the flow of convection. Whats left? Conduction and radiation.

In the case of windows, clear glass is transparent to radiant light, not 100% transparent, but enough so that you are losing heat thru the window glass to the tune of 60% of the total loss. This is real world this is not a lab setting.

LowE coatings effectively block that heat loss. It is measured, it is tested in real world, and it is not even an argument. It is 100% reality.

LowE coatings are so effective that the push today is to improve conductive performance of windows. That is where low conductivity spacers, triple pane windows, heat mirror, argon and krypton (and yes they improve CONDUCTIVE loss thru the glass by slowing CONVECTIVE currents in the airspace) come into play. Some of the newest technologies include vacuum glazing and aerogel both of which eliminate convective currents inside the IG airspace thus affecting conductive loss thru the glass.

LowE coatings are now standard for many companies, no longer an upgrade. To say that awnings may be less expensive is a massive stretch even if the coating wasnt free.

There is no standard for argon krypton loss in North America, however many fabricators test to a European standard (and I cant remember the number) that allows for 1% leakage per year. And yes, there is follow up testing in real world conditions on going.

Finally, you suggested that window performance numbers were artificially inflated in order to sell more windows? WHY? It isnt like there are options available. Window performance numbers are presented based on real life performance with the idea that performance varies under different conditions. Physics is physics and we are all subject to certain unbreakable laws, but there is no conspiracy to "fool people" into thinking that they are getting something better than it really is.

As an interesting thought experiment, what happens when the inner lite of glass in a window is warmer than the ambient air of the room? Using inside air temp 70 degrees, outside air temp 0 degrees and window glass temp 90 degrees, where is the heat loss and how does it get there?

While this whole idea sounds counter-intuitive to common sense, one of the more recent innovations in window glass performance to reach North America is heated glass.

Many folks would see that statement and immediately go ballistic thinking of all the wasted heat energy that would result from applying heat to window glass, however this has become the heat source of choice for many folks in Scandinavia and other parts of northern Europe.

And based on European performance numbers (and some US numbers now as well) there is actually very little heat loss to the outside, virtually all the heat stays inside the homehow would that work?


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RE: Repair, Don't Replace, Old Wood Windows

Good read again.

I will defer to Oberon again in this case as his explanation is (albeit more technical) my exact understanding of the dymamics and mechanisms of heat flow.

OLD, you are, in agreeing with me but in contrast to what you think.

My point about insulated walls (i.e. newer systems incorporating rigid foams especially) was to demonstrate that convective heat flow isn't even the dominant pathway in wall systems either. Conductive and radiant are. These are laws of science while I still agree with you that convection helps drive conduction and the resultant radiation, it is only a contributor and the final pathway of movement is conduction and radiation.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington

Let's look at how heat passes through an typical wood stud uninsulated wall with a typical uninsulated wall R-value of about 3.5.

The interior sheathing, usually 1/2" drywall, picks up head from the warm room air. This heat is distributed throughout the drywall by conduction. Gypsum board drywall has an HTC of .17 at 0 degrees Celsius. As good as a lot of insulation materials. But eventually the heat penetrates the drywall to the inner surface.

Inside the wall is air. Air picks up heat from the inner surface of the drywall and a convection current starts, similar to the illustration below. This convection current transfers the heat to the inner surface of the exterior sheathing, probably OSB in modern construction.

The OSB absorbs the heat from the convected air inside the wall and transfers it through a combined process of conduction and convection to the siding material. (There are air cavities inside OSB and both water and air inside wood -- both of which convect rater than conduct heat.) The siding, through conduction/convection finally moves the heat to outside air where it contributes its small fraction to Global Warming.

Obviously both convection and conduction are required for heat to escape through a wall. But DOE studies suggest that convection is responsible for 50-70% of heat loss. Conduction, therefore, is not the major player.

Admittedly there are interior sheathing materials with more insulation value than drywall, and exterior sheathing materials more effective at blocking heat than OSB or plywood. But such interior materials are very uncommon, and exterior materials often applied in addition to, siding, housewrap, and sheathing. We often use rigid foam along with exterior insulation for just this purpose.

But most wall insulation materials attempt to slow down heat transfer by interrupting the convection currents inside the wall cavity, not by reducing conductivity. The primary job of wall-cavity insulation is to dramatically slow the convection heat conveyor. If insulation does only that, it has handled most of the heat movement issues in your wall.

Wall cavity insulation slows convection by dividing the one big air cavity in your wall into thousands of tiny cavities or cells. Each of these cells will convey heat from warm side to cold side through the air trapped inside the cell, but thousands of cycles are required rather than just one big cycle. This greatly increases the amount of time it takes for heat to move all the way through your wall " as much as 20 times longer. Some materials are better convection-slowers that others, but all wall-cavity insulation focuses primarily on slowing convection.

Cavity insulation is the primary insulation in a stud wall. Layers of foam or other materials may be applied to the exterior surface, and there are even some materials that may be used inside. But no one suggests that surface- applied materials provide enough insulation to replace wall-cavity insulation. They are, at most, supplements.

So, I think I'm right. Convection is the primary source of heat movement through insulated walls, and will remain so until someone figures out how to eliminate air in wall-cavities.

In the end, though, except for the purposes of this discussion, it makes no difference which is the prime mover, both convection and conduction are required. So I agreed to leave it at that.

Have a great weekend,


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RE: Repair, Don't Replace, Old Wood Windows

Oberon,

Based on the e-mails I'm getting, someone is still reading this post. Of course, Nerds rule, didn't you know?

You make very good arguments, but you are just jabbing. Where is the knock-out punch?

Any proposition made in the general can be excepted in the particular. The general proposition that a steel ball when dropped will fall toward the center of the Earth is defeated in the particular instance in which a strong magnet is placed above the steel ball. This particular exception, however, does not negate the general rule.

The general rule of testing, especially product testing, is that the test environment must exactly duplicate the environment in which the product is to be used. If the test does not duplicate the actual environment in which the product will be used, any data derived from the test is invalid. This rule is so basic that no one argues the exception. It was drummed into me in Research 101 until I got sick of it.

Here is my thesis:

1. The hotbox environment used in most window testing - notably the NFRC protocol - does not duplicate the real world environment of a building envelope where the window will be used in that,

a. The testing protocol intentionally eliminates most convection effects from the testing environment, and

b. Most tests use a radiant heat source that is not found in most buildings. I have never seen a window in a building with a bank of heat lamps located just behind the window. Have you?

2. Consequently the data derived from hotbox tests cannot be used to predict how well windows will work is reducing the transfer of heat out of a building envelope. The hotbox data is flawed by the artificially limited testing environment.

3. Computer simulations and predictions of how well windows will work in retarding heat transfer are invalid because the data used to create the simulation and calculate the predictions is based on data derived from hotbox testing, which is invalid data.

4. Since hotbox testing focuses on radiant and conductive heat transfer, and eliminates most convective effects, the resulting data tends to overstate the effectiveness of window assemblies in retarding heat transfer.

If you can directly rebut any of the tenets of this thesis, please do so.

You may argue, as it appears you have, that the hotbox environment is no more artificial than the environment of the building in which the window will be ultimately used. My response is, so what? If the artificial hotbox testing environment is the same as the artificial building environment, then the hotbox testing would have some validity, but the artificial hotbox environment differs in significant ways from the artificial building environment, so the testing has little application to the artificial building envelope environment, e.g. the real world.

As to the particulars of your arguments:

I'm not sure what the argument about convection vs. conduction is all about. I agreed that glass conveys heat by conduction. In fact I gave the HTC of window glass.

But..

Convection, in the real world, is the prime mover of heat in a heated room to the glass, and convection is the primary mover of heat in the air (or other gas) between glass panes, and convection is the primary means by which heat is lost to the external air.

Yes, the exterior pane of glass will radiate, a little, but even more heat is lost to the air when the warm pane heats up air molecules in contact with the glass (by conduction). External convection is the process that ensures that a never-ending supply of cold air molecules is available to constantly take heat from the warmer external pane.

I understand radiation very well. Well enough to understand that in a net heating environment, it is not a prime player in heat loss.

Convection does not occur in a room only when the door is open, and closing a door does not block room air convection. It blocks only the temporary interruption in "normal" room convection caused by opening the door. Convection is ever-present in any gas or liquid above absolute zero unless the heat in the gas or liquid is perfectly distributed - and it never is. This convection is the process that draws warm room air to the colder windows of the room.

Low-e coatings are not "free", they are a part of the window price, even if no longer an "upgrade". Awnings and shades usually cost less than windows, but now I'm being picayune.

I have never thought of a house as a heat sink, but that's a good analogy.

The ISO Test for argon leaking that you refer to is, I believe, EN 1279-3 (Long term test method and requirements for gas leakage rate and for gas concentration). This test measures the ambient exchange rate between atmospheric gas and argon in an IGU. Some manufacturers use it, but no manufacturer that I can find actually warranties in-fill gas from leaking, because they know full well it will leak out over time. This warranty language from Milgard Windows is typical:


"For Milgard Products with argon or krypton gas-filled insulating glass, Milgard injects the gas at the time of manufacture. The gradual dissipation of the gas may occur naturally over time and is not a defect. Other than gas loss due to seal failures, this warranty does not cover the gradual dissipation of inert gas or the amount of inert gas remaining in the Milgard Products at any time after manufacture."

A warranty is a manufacturer's statement of how it actually expects its windows to perfom, and a solid gauge of how confident a manufacturer is in its windows. The absence of an in-fill gas warranty suggests that window manufacturers are not very confident of the long term survival of their in-fill gases.

How would heated glass panes be engineered to keep most of the heat in the house? Were I an engineer, I would probably place several low-e coated surfaces in the window on the exterior side of the glass. Heated glass is a radiant source, so you would want to block radiation from going outside and reflect any that tries back into the room. But them, as I said, I am not an engineer. I leave it to the boffins to figure things like that out. The studies I have seen show a lot of promise, but also a lot of expense to bring the product to market, a lot of expense to retrofit it into existing housing, and big bucks to buy the window. Of course, if it replaces central heating (which does not look possible right now), it would be worth it. What happens to your heat, though, when you install blinds over the window to deter nosy neighbors? That seems to be the big drawback of the technology. It only works if you live in the woods in Sweden where they don't seem to care about such things.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

If convection is the dominant driver of energy movement, why wouldn't a solid wall system (i.e. no insulation or air space be suitable)?

Dense packed walls or foam walls should show dramatic increases in R-Value then and much, much more consistent temperatures with air temp? The reality is that they do show some improvement but not appreciably when compared to a proper fiberglass wall. Why does Icyene foam have the same R-value that fiberglass does in an airtight wall if convection is driving the process.

None of your statements account for any radiant loss of energy. How is that possible?

Studs are the weak links (assuming equal air tightness) in most wall systems and that is a conduction and radiation shortcoming.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

There is no such thing as a solid wall system. Even foams and dense pack cellulose or fiberglass contain millions of tiny air pockets.

The fact is however, that dense pack walls do show a dramatic increase in resistance to heat transfer.

This was amply illustrated in a University or Oregon study of the actual R-value of 4" nominal wood stud walls, before and after retrofitting with dense-pack cellulose.

The clear wall* R-value of a nominal 4" stud wall with dense pack cellulose is R-15.35, while the clear-wall R-Value without the dense pack is R-3.22. The dense packing slows down convection by, as I stated earlier, converting one large convection cell into thousands of tiny air-filled convection cells. It takes heat much longer to traverse the thousands of tiny cells than it does to traverse 1 large cell, hence the dramatic increase in R-value.

Keep in mind that heat transfer cannot be stopped, it can only be slowed. The best we can do is a guerrilla-like delaying action. We can make it so hard to get out that it takes a long time. And that's the objective of insulation and other weatherization measures - making it harder for heat to escape so it takes longer.

The longer we can hold heat inside the building envelope, the less often we have to add heat. Without insulation, our homes can lose all their heat up to seven times each hour in winter. With adequate insulation and weatherization, we can reduce that to as little as once every three hours.

Note that the R-value of a typical dual glazed window with low-e coating is about R-2.5, which is lower than an uninsulated 4" stud wall at R-3.22. And there is evidence that the actual R-value of the window is less that the stated R-value.

Regards,



*Clear wall R-value, by the way, takes into account the thermal breaks caused by framing members. Without the thermal breaks, the center of cavity R-Value of the cellulose cavities alone would be 16.9. For an explanation of Center of Cavity vs. Clear Wall vs. Whole Wall measures of R-value see R-value, U-value... What Do They Mean?.


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RE: Repair, Don't Replace, Old Wood Windows

Xoldtime,

Lets assume from here on out that we all understand insulation. The conversation will move along faster without having to go back and give definitions of explanations that both of us know (i.e. insulation is trapped air in whatever the matrix is).

When I was referring to a solid wall, I was speaking to the idea of single sheet of wood that provided both the air barrier and structure (i.e. a 3" solid plywood sheet or similar). Another example could be an aerogel wall system or window with no airspace separating the two layers.

In that application, there is no interstitial wall space or convection inside the wall/window system. What is the dominant pathway of loss in that application....conduction and radiation. These are not really points of debate but part of the laws of energy transfer.

Regardless of the reduction of convective movement, the energy transfer through a given solid substrate is conduction and radiation on the other side. How fast that energy can be picked up and moved away is assisted by convection.

R-2.5 does not even come close the performance of most good, double pane IGU systems.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

In the situation you posit conduction and minorly, radiation would be the only heat transference methods through the wall.

R-2.5 is low for a good dual panel thermal window units, but on target for the average unit -- and about 80% of the windows sold in the U.S. are no better than average -- especially builder windows in new houses.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Xold,

I think you just made my point for me then.

Most windows are sealed units and inert gas filled so convection is greatly reduced and the temperature differentials of glass surfaces, driving convection, is as a result of conduction and radiation.

Agree that builder's grade stuff is garbage, however, that was never part of the comparison or a player in the analysis for replacement vs. repair discussion.

In either case, we will probably have to agree to disagree in this case.


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RE: Repair, Don't Replace, Old Wood Windows

Xold, you are incorrect, again. The average U-factor for a double pane glass window with LoE and argon gas is .30. That translates to an R-value of 3.33. There are more and more windows being made that even exceed the .30. Okna has one that gets a U.25, which trnaslates into n R-4. This will be increased in 2015 once the R-5 Energystar requirement program goes into effect. Our Northern Virginia company is already heavily promoting R-5 windows and the response has been very good.


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RE: Repair, Don't Replace, Old Wood Windows

I think xoldtimer has underestimated the dangers of lead based paint.Even though ingestion is the most common way for a child to become poisoned, dust is a very likely source from hand to mouth contact.simply vacuuming it up and trapping it in your HEPA vac will not remove the hazzard most of the time. Surfaces such as floors,window sills,window troughs can be very pourous and very hard to get clean to levels belows HUD standards. Lead poisoning is often chronic from very small amounts of lead being ingested over time.Windows can pose a great threat since they are one of the most common component to contain lead and they are a friction surface that generates lead dust.


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RE: Repair, Don't Replace, Old Wood Windows

"I think xoldtimer has underestimated the dangers of lead based paint."

And you seem to be greatly exaggerating it.

It is NOT as common as the EPA would have you believe, and lead poisoning in children has been consistently falling since lead was removed from gasoline.

Lead containing paint was always expensive paint, and full gloss (the lead component is lead acetate, AKA 'sugar of lead' added as a drying agent and gloss improver).


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RE: Repair, Don't Replace, Old Wood Windows

I agree that the dangers of lead paint have been overblown by the EPA. In addition to levels of lead poisoning in children in decline, the figure that is often touted by EPA is inflated as it's not claiming the contamination is coming from "friction from windows". I think it's more likely coming from children ingesting lead paint from chips peeling off interior walls and ending up in their food or children simply eating paint chips. I recall when this used to be the claim when environmental groups like the Sierra Club were on their campaign to ban lead paint.

I think the long term financial impact on the consumer due to the added cost of lead containment procedures by a certified contractor causes many people to delay replacing their windows. Or they simply find a contractor who's willing to circumvent the law. The only entity that suffers is the concerned homeowner and/or the honest contractor.


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RE: Repair, Don't Replace, Old Wood Windows

Xoldtimecarpenter, oberon, windowsonwashington, skydawggy: I'm still reading this thread, which makes me some sort of geek! But an appreciative one, since it is taking us years to formulate our plan to restore our house's windows
Lynn


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RE: Repair, Don't Replace, Old Wood Windows

Lead paint chips falling off the walls and landing in there food is highly unlikely, but probally hard to prove since the evidence is gone.The highest levels of lead dust are statistically in the troughs (wells) of windows.There is a reason the EPA specifically singled out windows in the RRP rules.The dust poses a threat due to the hand to mouth contact from things that come in contact with the dust. Although eating lead chips is a common way for children to become poisoned dust is considered to be more so.It is not okay for a homeowner to power sand the exterior of there home and let it fly just as it is not ok to remove a window without following the rules. As far as being a money grab that is up to the contractor,it hasn't effected my pricing very much at all since I have been using lead safe work practices for years.The only thing I wasn't doing was the dirty diaper test and it's documentation.Anyways these hazzards are real and it is a little discerning to see some real stupid advice being given out.
Brickeye, yes,ok lead paint is/was expensive.


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RE: Repair, Don't Replace, Old Wood Windows

I appreciate the theoretical discussions! However, can anyone point to a good educational resource for all the steps and materials one might apply to restoring windows? I have ideas, I believe I can do this (I am pretty handy), helped my grandfather do this 40 years ago (but forgot much) but I would like to give this is a shot. Thanks in advance.


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RE: Repair, Don't Replace, Old Wood Windows

I have a number of links, the best thing will be for you to browse them yourself to find what works for you. (Since there are 3 I'm not going to select one to become an actual link - you get to c&p all of them!)

This guy is a big advocate for window restoration. A lot of his stuff is for purchase but there's plenty of free information there, too.

http://www.historichomeworks.com/hhw/index.htm

The OHJ web site is a treasure trove and there are some informative people participating in their forums.

http://www.oldhousejournal.com/

OHJ has a selection of federal documents on historic preservation. There is another section on the site with archives of their articles. You'll have no trouble finding it.

http://www.oldhousejournal.com/npsbriefs2/

Have fun!


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RE: Repair, Don't Replace, Old Wood Windows

We're currently restoring our old original-construction (1894) rope & pulley windows, and have managed everything about it--including removing 117 years of paint holding the windows shut. The next step is figuring out how to remove the press-in sash pulleys for reconditioning or replacement. Anyone have any suggestions for us--besides removing the entire window frame to get at the back side of the board in a convenient position?


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RE: Repair, Don't Replace, Old Wood Windows

"Lead paint chips falling off the walls and landing in there food is highly unlikely..."

Especially since very few walls and ceilings are painted with gloss paint.


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RE: Repair, Don't Replace, Old Wood Windows

Lead paint could be had in other sheens besides gloss.Baths and kitchens would be more likely to use gloss paint.
As for the pulleys, they will be pretty hard to get out with destroying the pulley.i would try a sharp chisel to get between the wood and the pulley and lift the bottom or top edge out. I would use a nail puller to grab the corner and pull it out a little at a time alternating from top and bottom.You could also use a vice grip or whatever.This method would destroy the pulley,which would make a good reason to uprade to a nice cast pulley. The cast pulley would have to mortised in but would be worth the effort.


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RE: Repair, Don't Replace, Old Wood Windows

"Lead paint could be had in other sheens besides gloss."

Rarely.

Lead pigment diapered long before lead acetate (AKA 'sugar of lead') from gloss paint.

It was added as a drying agent, hardener, and gloss improver.

None of these things benefited flat paint significantly, so it was rarely used.

It is the lead acetate in gloss trim paint that is almost all the hazard.


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RE: Repair, Don't Replace, Old Wood Windows

Well as rarely as it is I will be working on a house that has lead paint in the kitchen walls and ceilings and rear stairwwell walls.This house has a child with elevated blood lead level as well.The other walls and ceilings may have lead as well, but I have not seen the full XRF report yet.The child is thought to have been poisened from bare soil in yard though.Even though it may be rare it is not uncommon,especially in homes built up to the 1930's.


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RE: Repair, Don't Replace, Old Wood Windows

Kitchen, stairwells, closets, and trim are all common places to find gloss paint.

There is no reason to even consider removing it from walls.

Put another coat of paint on to encapsulate the lead containing paint.


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RE: Repair, Don't Replace, Old Wood Windows

So when you say very few walls and ceilings are painted with lead paint, you now mean very few walls except kitchens, baths, stairwells and closets? There can be many reasons for removing it or enclosing it."Encapsulating" lead paint is a bit more involved then just putting a coat of paint on it.I would maybe do a little more research before making any other comments.
I started a house today that has plaster walls and ceilings in the basement laundry that also have lead paint on them.This is another place that lead paint is often found.


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RE: Repair, Don't Replace, Old Wood Windows

""Encapsulating" lead paint is a bit more involved then just putting a coat of paint on it."

N, inm,ayu cases that is all that is required.

Kitchens, baths, stairwells and closets often had gloss paint applied.

Those are very small portion of a typical house, and not that many residential stairwells have gloss paint.

Flat paint has not used lead for a very long time.

It is the gloss paint that is the common hazard.

Look up lead acetate and its uses.

The fact that child blood lead levels have fallen exactly as the use of lead tetra ethyl in gasoline has fallen indicates most of the EPA claims that lead paint was the common source of childhood lead exposure was simply incorrect.

Leaded gasoline spewed huge quantities of organic lead compounds into the air, and in cities was likely the real source.


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RE: Repair, Don't Replace, Old Wood Windows

I don't know what N,inm,ayu cases refer to.The process for "encapsulating" and merely painting with paint or an encapsulant paint are completely different and should not be confused. I think agree with you a very few walls being painted with Lead paint but you seem to be all over the place with what is few and what is common.My point is one should not assume a wall or ceiling not to contain lead based paint regardless of location of walls and ceilings nor by sheen in pre 1978 housing.
The EPA's website does specifically states that Lead from gasoline as a likely source of lead inside and out of a home.


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RE: Repair, Don't Replace, Old Wood Windows

@GRhouse, You asked how to remove the pressed-in (tin?) window pulleys. They will often have been secured with a sliver of wood or dowel through both pulley centers, as they line up more or less with the unseen surface of the side jamb wood, and have a hole straight through. As you have witnessed there are no visible fasteners on the room side. The top and bottom edges of the pulley housing were also barbed to grip the drilled mortise, but when/if the fit was not sure, the carpenter would slip in a sliver of wood.
Casey


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RE: Repair, Don't Replace, Old Wood Windows

Thanks, sombreuil mongrel, for the information about how to remove the pressed-in sash weight pulley. We won't have time yet this year to take care of them now, though. So I'm using my Moto Tool with wire brushes to clean them up, in place--what fun! They won't look as nice as the $80 each set 4 of Decorative Windsor Pattern cast bronze ones we really want. But how many people are going to look at the sash pulleys?


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RE: Repair, Don't Replace, Old Wood Windows

"...pre 1978 housing."

This is gross exaggeration by the EPA, congratulations on taking the hook.


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RE: Repair, Don't Replace, Old Wood Windows

brickeyee....did you get my email?


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RE: Repair, Don't Replace, Old Wood Windows

What is N,inm,ayu cases?


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RE: Repair, Don't Replace, Old Wood Windows

I just want to thank any or all of you who posted here about how to repair old windows with sash weights and pulleys. Today, if our weather holds off on 20% chance of rain, we should be able to install the spring bronze weatherstripping on the last side of the upper window and reinstall the reconditioned upper sash. The whole window looks beautiful, and the lower sash (which is all we've got installed as yet) works beautifully--slides up and down very smoothly over the spring bronze weatherstripping. So, thanks everyone who gave me the clues on how to do this.


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RE: Repair, Don't Replace, Old Wood Windows

Nothing quite like a smooth running weight and pulley system, even large windows open with one finger and the sound can't be beat.Pictures would be great.


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RE: Repair, Don't Replace, Old Wood Windows

Attn: toddinmn. Would love to send you pictures. However, my computer and I are having a major disagreement about sending photos via email. So far, it's winning. By the way, I assume from your user name, you live in Minnesota. Whereabouts?


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RE: Repair, Don't Replace, Old Wood Windows

Post pack with some pictures of the completed "tune-ups".

I love the look of original, air tight, wood windows.


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RE: Repair, Don't Replace, Old Wood Windows

I am in Brooklyn Center, raised in Hutchinson.Let me know if you are looking any pulleys, always tearing out old ones and may have a line on some new ones.


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RE: Repair, Don't Replace, Old Wood Windows

I wonder if anyone has looked at 4 windows, side by side, in a home and 1 window is a new vinyl, double pane, no gas fill, 1 is double pane, argon gas, 1 is triple pane with krypton gas and an old window that has been "completely restored" and used an infrared camera on them at the exact same time to clearly differentiate the heat savings, or lack thereof, of all these windows. Has such an experiment been done? I would love, along with others, to see the results.


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RE: Repair, Don't Replace, Old Wood Windows

The results would most certainly show the following order from warmest (assuming cold temperatures outside) assuming your are figuring on Low-e in all of the:

-restored wood with an air tight storm would be the warmest (i.e. losing the most energy from inside)
-double pane sealed with Low-e would be next
-double pane sealed with Low-e and argon would be next
-triple pane with Low-e and krypton would be last


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RE: Repair, Don't Replace, Old Wood Windows

Actually, based on field studies, the restored single glazed wood window with storm would perform better than the dual-pane IGU. See, e.g.:

Testing the Energy Performance of Wood Windows in Cold Climates: A Report to The State of Vermont Division for Historic Preservation, Agency of Commerce and Community Development
, University of Vermont, Vermont Energy Investment Corporation, U.S. Army Cold Regions Research and Engineering Laboratory, 2009.

The argon- and krypton-filled windows would work better than the restored wood window with storm only as long as the fill gas lasted, then they would be no better than an typical, air-filled, dual glazed thermal window. And there is no question that fill gas is going to leak out over time, sometimes after a very brief time. Gas filling is a measure used to temporarily inflate the thermal performance of windows so they seem to be more efficient than the actually are.

"No manufacturer warranties in-fill gas from leaking, because they know full well it will leak out over time. This warranty language from Milgard Windows is typical:

'For Milgard Products with argon or krypton gas-filled insulating glass, Milgard injects the gas at the time of manufacture. The gradual dissipation of the gas may occur naturally over time and is not a defect. Other than gas loss due to seal failures, this warranty does not cover the gradual dissipation of inert gas or the amount of inert gas remaining in the Milgard Products at any time after manufacture.' Your Old Windows: A Consumer Guide, StarCraft Custom Builders, 2010.

When Milgard says "gradual dissipation of the gas may occur" they are being disingenuous. What the company actually means is "will occur", because there is no recorded instance of in-fill gases that did not leak out over time."

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

And here we go again....

chipster_2007,

Feel free to re-read the thread when you have some free time. Oberon and I have hashed this thread and question out pretty thoroughly.

The R-Value of a single pane wood window with a tight storm window (most are not) is about an R-1.85 on average. R-Value of a decent insulated glass IGU without argon can easily be an R-3+. R-Value of a double pane window with Low-e and argon is R-4.

Triple pane R-Value with argon can easily exceed R-5+. Triple pane krypton number are R-6.5+ in some cases.

Numbers are what they are despite the convection arguments.

http://www.finehomebuilding.com/how-to/articles/understanding-energy-efficient-windows.aspx

http://www.coloradoenergy.org/procorner/stuff/r-values.htm

Here is a link that might be useful: Good Read about windows


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RE: Repair, Don't Replace, Old Wood Windows

Argon in windows does not make a big difference in U/R values, the biggest gains come from Low-E coatings.
aproximate U-values:
wood single glaze with storm .50
wood single glaze with Low-E storm .36
vinyl clear dual pane IG .48
vinyl Low-E .33 dual pane
vinyl Low-E/argon .30 dual pane
wood sash kit clear dual pane with storm .34
wood sash kit with low-E/argon dual pane with storm .24
Figuring out actual cost saving between all of these is a black art especially when you start throwing in air infiltration numbers, SHGC numbers, condition of windows, brand of storm windows and of course who is doing the testing.Just remember liars use statistics and statistics lie.That being said, I would do what is best for you and your house and not worry about the numbers to much because your old house is probally losing more money through air leaks and insulation inefficiencies.


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RE: Repair, Don't Replace, Old Wood Windows

+1 to Todd's post.

Figure out what is right for you home. Air infiltration and air tightness are the variables in this equation that can throw the U/R numbers way off.

That is in large part the benefit of a sealed IGU (insulated glass unit, i.e. double or triple pane). The fact that the air is dead air and not moving.

It can be very difficult to get a sash pack replacement in and make it air tight whereas most folks can get inserts in and make them tight.

If the window is at all historical or maintains the look you are wanting, a Low-e, insulated storm, is a great option when combined with retrofitting the existing window. That scenario, although not referenced in your initial question, will give you very good R-Values.

I will disagree with Todd slightly in that Argon has been shown to increase the overall IGU efficiency by about 20% as compared to an air fill. Example, a window with an air fill might be a U-Factor of 0.35 whereas it will be a U-Factor of about 0.30 with argon.


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RE: Repair, Don't Replace, Old Wood Windows

That link you posted OTC is a perfect example of someone setting out to prove a point and then completely ignoring anything that is counter to their pre-determined conclusion. It's so full of holes that I stopped reading it after several pages. i'd lie to have that part of my life back.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

"That is in large part the benefit of a sealed IGU (insulated glass unit, i.e. double or triple pane). The fact that the air is dead air and not moving."

What?

Not so! Air between the panes of an IGU is moving constantly and conveying heat in the process.

"The R-Value of a single pane wood window with a tight storm window (most are not) is about an R-1.85 on average."

I have seen this figure (and others) tossed around as the R-Value of a single pane windows with storm, but I have found no authoritative source for it. If you know of a report of an actual laboratory test of an spw w/s, I would love to read it. I have never found one, and believe me I have looked.

I agree that a dual glazed window can reach an R-value of 3+, but the operative word is "can", not "will". Most average around R-2 ro 2.2 in the perfect, controlled environment of the testing lab. What they rate in actual use is anyone's guess since they are never rated in actual use.

I don't think is correct to assume that most storm windows are not tightly sealed any more than it is correct to assume that most replacement windows are improperly installed.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

I was not speaking to convective looping but moving in and out of the IGU like the air between a storm window and window move (i.e. to outside).

We have had this discussion on multiple occasions and you referenced any number of my previous posts, you would quickly realize that I was not suggesting that the gas or air fills inside a seal IGU are static.

How can you dismiss what is pretty universally accepted as the R-Value of a single pane wood with storm window combination in one breath and claim that an NFRC thermocouple measured window will only perform at 60% of its intended value in "actual" use.

Wouldn't the same strains placed on a window in "actual" use just as adversely affect the single pane wood and storm combination? Even more so negative would the impact be given that it is scientifically proven that a storm/single pane window is not an airtight combination and the insulation value of that trapped air, much like air moving in fiberglass, is seriously diminished when the air is lost to outside.

In terms of those people quoted R-Values of 2 (which is generous given the questionable air tightness mentioned above), here are some links. They don't reference the study that they used to establish this guideline but I hardly consider secretive fact.

http://www.efficientwindows.org/glazing_.cfm?id=3

http://www.coloradoenergy.org/procorner/stuff/r-values.htm

http://chicagoconservationcorps.org/blog/weatherization/education/windows-and-heat-loss/

Storm window in no way shape of form approach the tightness of a sealed IGU. They must accommodate movement and therefore rely on weatherstripping and other seals against air loss. They only have thin interfaces with the frames and do not have the same weatherstripping profile flexibility as the operable window. Most are not nearly as air tight as even the leakiest windows. This leakiness is what drives the efficiency of an otherwise suitable combination down well below that of a sealed IGU.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOnWashington,

Yes, I've seen these sites before.

Efficient Windows Cooperative reports the R-value (actually U-Value) of single glazing (center of glass value), but not with storm window.

The other two report that the R-Value of single glazing with storm is R-2.0, a number commonly quoted, but they don't say where they got that number.

I'm still looking for the actual study that tested single glazed windows with storms and found a R-value of R-1.85 or R-2.0 or whatever. I'd like to know if this is the whole window r-value or just the center of glass R-value, and the methodology used to calculate the R-value.

Just because a lot of people say something, and say it often and loudly, does not mean it's correct. In 1491 everyone knew the world was flat, the sun revolved around the earth, and that our planet was the center of the universe. Turns out, however, that none of it was true.

You might take a look at Joseph H. Klems, "Measured Winter Performance of Storm Windows", Lawrence Berkeley National Laboratory, (2002) (Download (PDF), in which the R-value of a single glazed window with storm was calculated under field test conditions to be R-3.01.

The study is interesting for its methodology which suggests that test environments much closet to the real world environment can be constructed to produce window ratings that are much more applicable to real world installations.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Xoldtime,

There was no mention in the article of what the claimed U-factor on the single hung replacement was.

From your study.....
When one compares the values in either the measured or corrected column of Table 4, a recognizable pattern emerges: the addition of either low-E storm produces a combination that has performance close to, but not quite as good as, that of the replacement window.

Actually, the data that if referenced in you study indicates and R-Value of 1.72 (U-Factor W/m2K = 3.32) for a single pane window with storm. Single pane with storm and Low-e has an R-Value of 1.87.

These numbers are from your quoted study. R-Value of the replacement window is this case was measured at and R-Value of 2.28 (roughly 22% better by comparison to the single pane with storm window and Low-e and 33% better than single pane with un-coated storm).

This study was done circa 2002 when the Energy Star for that region where the window was tested (Reno, NV) was U-Factor of 0.40 (R-2.5). In this comparison, the replacement window was function at nearly 91% of its claimed performance.

This somewhat negates your claim that the static testing done by the NFRC is unrepresentative of real world numbers.

As a matter of fact, in this study, the author specifically mentions that the connection between the wall and the replacement window was compromised and did leak air although he mentions that the air leakage on both assemblies had little effect on total thermal performance. Therefore, a properly installed and sealed (foam, backer rod+sealant, sealant) replacement window would perform even closer to its claimed R-Value and further lengthen the gap between the storm and single pane combo.

I find this a bit questionable given my personal observations but this is what the study claims. The test case windows were on the shielded side of the wind.

Leakage of the single pane window was designed to be average. In order to achieve that average rating, you, in most cases, will need to retrofit that window. Using a tighter exterior storm with a looser interior window will result in condensation and storm window sweating. Making the exterior storm leakier to accommodate for leakage and prevent sweating will further reduce the R-Value of that assembly.

If you take the same real world vs. claimed performance representation of 91%, this would mean that double pane windows available today with an R-Value of 4 are actually near 3.64. This would put newer insulated windows at better than 2X times the performance of a single pane wood with un-coated storm.

These numbers are from your study. Before you challenge anything that I have written, I would suggest you re-read the study.


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOn

You are right about the R-value. I don't know what number I was reading when I wrote that. Actually, I do, but I won't get into that.

I don't disagree with much of what you said. After all, it's right out of the study.

The one thing I will note is that the air infiltration effects were not accidental, they were deliberately introduced to see how much impact they had on overall performance.

We don't know what the NFRC rating of the test window was. It may or may not have been up to the Energy Star minimum, so you cannot compare the window's performance under these test conditions to a supposed NFRC rating. Without knowing the NFRC rating of the windows we can conclude nothing about the relation of NFRC testing to window performance in the study. So I must discount that argument, sorry. Good argument, though.

Back to the real world. You indicate that the dual-pane thermal window performed about 22% better than the window/storm window combination. I can accept that with the observation that this makes little difference to real world performance.

The difference in tested performance between the window/storm and dual-pane was R-0.41. How much are you willing to spend to get an improvement of R-0.41 over your existing windows?

Should I replace my old wood windows or should I repair and restore them? Ultimately that is the question to be decided.

Let's look at the numbers from my house. I have 27 oak wood windows. Replacing them all with a comparable oak wood dual-pane double-hung window (Kolbe Heritage Old World Series, or equivalent, no fill gas, hard low-e), including installation, would cost me about $1,200 per window (and that's with my dealer discount) or $32,400. This would give me a window with a rated U-.33 in the NFRC tests, or R-3.

Or,

I can restore and weatherproof the existing windows at an average cost for labor, materials and taxes of $271.42, then add a very good, color matched, low-e storm window for a cost of $97.32, including installation, for a total of $368.74 per window or $9,955.98 overall.

Which way to go???

If I go with the Kolbe windows,then I get an additional R-1.15 per window at an added cost of $831.26 per window, or a total added cost of $22,444.02.

Or,

I can suffer through with a mere R-1.85 per window and pay an estimated (by my local utility) additional $70 per year for heating and cooling my house. After 50 years, I will have paid an additional $3,500.

To recover the additional cost of the Kolbe R-3 replacement windows from energy savings on my heating/cooling bill, I would have to live another 321 years. And, while I am in pretty good shape for a broken down ex-Marine, I would have to give very long odds of that happening. (But if it does, I plan to create my own diet and exercise program on DVD and make a killing through infomercials.)

Throughout this whole thread, this is really the only point I wanted to make. Maybe I did not do a good job of it, but that is the only point.

Replacement windows are greatly oversold as thermal products. The fact that a replacement window has a rated thermal performance of 22% or 122% or even 222% more than my restored old window makes but a few dollars difference in performance in the real world.

While NFRC ratings overstate the actual installed performance of thermal windows, typically modern windows do in fact perform somewhat better at inhibiting heat transfer than restored old wood windows, at least in the short term. But they don't last hundred of years like traditional wood windows, cannot be easily or economically restored or repaired when they finally do fail, and do not provide a sufficiently better thermal performance to make the investment in replacement windows worth the enormous cost.

That may change, but at the moment restoring old windows is almost always the better economic and aesthetic choice.

Always a pleasure,



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RE: Repair, Don't Replace, Old Wood Windows

Most people are not going to have Oak sashes and nor are they going to use $1200.00 windows.My cost on a decent vinyl window is around $200, wooodgrain add 25%.Cost on a Marvin Ultima insert is around $450.Cost on a Sash kit is around $225.It is misleading to take a worst case scenario and presenting it as the almost always better economical solution.


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RE: Repair, Don't Replace, Old Wood Windows

+1 to Todd's comments. Todd, shoot me an email when you get a chance.

Xoldtime,

Could of points to address.

The air infiltration was noted to minimal impact but the windows were placed on the non exposed side of the building so they were not getting hammered like they would on the other side. They also noted considerable leakage between the frame of the replacement and the framing of the test building. A properly installed replacement window should not be leaking at that connection and a tighter window connection would further create better performance for the replacement window.

Nest, the study specifically references the fact that they used a vinyl single hung with soft-coat Lowe-e/argon combination. I made the assumption that the window was Energy Star (U-0.40) for the sake of argument and it actually shortened the spread between the comparable R-Values of the windows compared in this case.

If you are saying that the window was not Energy Star Qualified, that makes the data even more favorable looking for the Low-e/Argon replacement because both the R-Value improvement and NFRC claimed value and real world R-Value that much better.

These two arguments that:
-NFRC values are unrepresentative of real world performance figures (i.e. convective looping, etc)
-Single pane/storm windows have as good a thermal performance as replacement windows

are now resolved and determined to be largely incorrect by the very study that you posted.

As I mentioned in my previous post, the newer performance packages with R-4+ numbers out of double pane and R-6+ out of triple pane are going to even further lengthen the spread between single pane/storm and replacement performance.

I agree with Todd that your numbers are very unrepresentative of real world numbers and you can skew the numbers to legitimize any comparative analysis.

So we can put this argument to bed for the last time...............I think that the wood window restoration is a good and viable option!!!!

If the window is in otherwise good shape or a historic application, getting a storm or insulated storm window is a great option.

That being said, most of the wood windows that will require replacement are from young growth timber and are rotting in multiple locations, poorly constructed, and certainly not worth repair. Most clients in that case are very happy with a good vinyl replacement.

I think your prices are a bit off on storms but lets use your number of $370 for retrofit and a number $550 for a very good vinyl replacement. In this application, the replacement will have a 2X better R-Value and I can guarantee you save more than $70 per year if you figure on the overall R-Value impact on the wall.

Combine the added R-Value with the functionality of the new window and most customer with non-historic wood windows would probably opt for the new replacement and in this application I would theorize that the ROI differential is probably less than 10 years by comparison.

Again, I think restoration is a fine and suitable option when dealing with historic windows and good wood. That just represents such a small portion of what is out there that it does not enter the conversation in most cases.

I have never argued that point and if you look at other posts, you can see where I have recommended that option. I am all about preservation of existing materials if they are candidates.

Windows aren't even the first thing on the list of things to do in most homes energy efficiency retrofits anyway.


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RE: Repair, Don't Replace, Old Wood Windows

Toddinmn, welcome to the discussion.

You said:
Most people are not going to have Oak sashes and nor are they going to use $1200.00 windows.My cost on a decent vinyl window is around $200, wooodgrain add 25%.Cost on a Marvin Ultima insert is around $450.Cost on a Sash kit is around $225.It is misleading to take a worst case scenario and presenting it as the almost always better economical solution.

Unfortunately your argument is an old lawyer trick we all learn in the first week of law school: "If you don't like the answer, change the question."

First, there are no "decent" vinyl windows that wholesale for $200. These are bottom of the line windows. A "decent" vinyl window, if there is such a thing, will run about $350.

If you reread my post you will see I posited replacing my existing windows with "comparable" quality windows. Plastic windows are not comparable to oak wood windows.

To reach the quality of my existing windows in terms of materials, workmanship, and functionality you are going to have to look at a top-of-the line window. I like the Kolbe window because it is will made, uses gravity balances, and can be made reasonably thermal resistant. At a retail of about $1,200 it's actually a bargain. My single panel wood windows cost an average of $100 in 1928, which is $1,326.84 in today's dollars. Kolbe's windows are dual pane, with a triple pane option, and low-e coated. Much more value for a lower price.

My restored windows will easily last another 100 years. Your plastic windows will last, with luck, 30 years.

Anyone can replace a good quality restorable wood window with an El-Cheapo, Inc. plastic window. But if you are doing that, then you are not doing your customers a service.

We prefer to have our customers come back.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

WindowsOn

As usual, you make some good points.

There is considerable research support for the proposition that single pane primary windows with storms (SPPW/S) can outperform dual glazed windows, see, e.g. the Vermont Study. Do the always do so? No, of course not. But when dual panel windows outperform SPPW/Ss, they do so by such a tiny margin, that in real economic terms it translates to not much savings in energy costs compared to the relative high cost of replacing the window. Again I refer you to the Vermont Study which found that the annual energy savings of replacing a SPPW/S with a dual-pane low-e windows was only $4.45 per window.

I will state again that since NFRC ratings of the test windows in the Hill study are unknown, we cannot infer comparisons between the study R-values and some hypothetical NFRC testing R-value. But, assuming (notice the "assuming"), the windows were up to the Energy Star standards of the time, then the study R-values were lower. If the windows were not up to the Energy Star level, maybe, R-2.2 or so, then the study R-values were lower. So, how does this refute my position that NFRC tests tend to inflate R-values? If you say "well, they were only inflated a little", ok, but still they were inflated. Of course, I don't think any such conclusion can be drawn from this study. The data are not there.

...most of the wood windows that will require replacement are from young growth timber and are rotting in multiple locations, poorly constructed, and certainly not worth repair. Most clients in that case are very happy with a good vinyl replacement.

We don't run into many of these in this area. Our pre-war housing seems to have pretty good wood windows made from, dense, old-growth timber with excellent craftsmanship. In the pre-war housing I saw in the D.C. area when I was working there, it was not true either.

Any customer, who having been honestly presented with the options, carefully explained, who then replaces his or her heritage wood windows with plastic windows is certifiable, and deserves what he or she gets. Most, however, in my experience, and we do carefully explain the options, elect restoration. Does your company even offer restoration? If not, then I doubt you talk about the possibility of restoration in your sales presentations. Naturally, if not aware of the possibility of restoration, a customer will elect replacement, but only because he is unaware of the option of restoration.

In 40 years I have not run into a wood window that cannot be restored to as good as new, and for a lot less money than it would cost to replace the wood window with one comparable in materials, workmanship, and longevity. In the older parts of the country where the housing is also older, this may not be true. But it was true of pre-war housing in the D.C. area in the 1970s when I worked there. When I was making my modest contribution to the volunteers who restored housing parts for the Smithsonian at Silver Hill, MD, I saw some truly deteriorated windows, but none we could not repair.

Heritage windows are not rare, as you seem to think. Half of U.S. housing was built prior to 1974, and over 20 million still-occupied houses were built prior to 1940. Almost all of these started out with wood windows.

And that, sir, is my final answer.

-----------------------------------------------------------

I started this thread over a year ago to generate some discussion about restoring rather than replacing heritage wood windows.

The discussion has been exceptional beyond any expectation I may have had, with numerous, well reasoned and well written contributions from some very knowledgeable people, such as yourself.

I learned some new things, and I hope those who persevered in reading through all these posts did as well. I think every point of view has been extensively and fairly represented. And I appreciate the substantial, well-presented, contributions of all who participated.

But now I have to go back to taking care of business.

It has been fun, best wishes to all, and adios.

Regards,


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RE: Repair, Don't Replace, Old Wood Windows

Xoltime,

I don't know where you get some of your information but your response to Todd was totally incorrect.

You can purchase a decent vinyl window for less than $350 everyday. I would suggest your take another look around (of course you would prefer death over a vinyl window).

There is absolutely no research to indicate that the premium vinyl windows that are out now will only last 30 years. Even if that where the case that is about 2X longer than most of the wood window that we see being produced now.

+95% of the wood window stock that is out there now (that we see) is not serviceable and we would be doing our customer a disservice to try and fix a failing and poorly built wood window.

You claimed that NFRC inflated their values. My point was that if the lack of convection and other "real" world environment showed a lesser R-Value, it was slight, if at all. Given that we don't know the claimed U-Factor of the window in question, I was assuming that the window was Energy Star (U-Factor 0.40). If the U-Factor was higher in the study sample, the window would be performing at very near claimed thermal data (91% of claimed value was based on the assumption of an Energy Star window).

I think the fact that the window was operating at nearly 91% of Energy Star (again, assuming their window was Energy Star) is pretty darn close and indicates that the NFRC is not inflating values at all. The NFRC values are not based on dynamic environment (i.e. air leakage...which there was considerable amounts of in the replacement windows connection to the home in this case).

You have long argued that the NFRC values where off and were unrepresentative of real world data. Without re-reading the entire thread, I seem to recall you claiming that real performance was at a delta of close to 40%, whereas your study indicates a very slight change of less than 9%...again with a bunch of leakage that should not have happened.

If you haven't seen a window that can be restored for the same price as a replacement, you haven't been on any customer visits with me. I would welcome you to come with me and take a look at the wood window stock that is prevalent in our area and we can record your reaction and assessment and post it up for mass consumption.

Couple that with the fact a vast majority of customers don't like storm windows, their old windows, and the misc. issues associated with them...more of the inclination to replace comes from the customer.


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RE: Repair, Don't Replace, Old Wood Windows

xoltimer, Sure start a post guaranteed to start an argument then bail out.Just kidding, well sort-of kidding anyways.


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RE: Repair, Don't Replace, Old Wood Windows

This thread is valuable even a year later since the issue discussed comes up all the time. We want to retain the look of the windows in our house, so the decision is to renovate and repair the windows and stop the air infiltration since the windows were undoubtedly not foamed and sealed to the rough opening properly. Window contractors want to replace all the windows (of course). Our problem is to find craftspeople who can do the work.

Let the nerds run the world!


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RE: Repair, Don't Replace, Old Wood Windows

We have what I believe is called a colonial style bow window. It's comprised of 20 separate single panes of glass within a wooden frame. The house was built in 1965. We like the look of the window.

After reading the discussion on restoring old windows, I am considering the replacing of each of the 20 individual panes of single glass with individual sealed units.It would be good to hear back from people who have attempted to do this. My concern is that I do not have a lot of room to work with, once I remove the existing stops. If I use 1/2 inch sealed units, I will only have room for 1/2 inch stops. The concerns are: 1) is a 1/2 inch deep wooden stop strong enough to hold the glass?; 2) will I get much resistance against heat loss from 1/2 inch glass units?


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RE: Repair, Don't Replace, Old Wood Windows

Built in 1965, I doubt that you could not find something new that can replicate that look. As discussed earlier in this thread, there is certainly some gain to be had by replacing single pane glass with double pane, and 1/2" stops are more than adequate, however I'd have the following primary concerns:
-you are adding a tremendous amount of weight to the overall unit that was not designed to handle it.
-20 ig's even if small, would end up being rather pricey. Those are also 20 potential seal-failures.

.... You might consider posting this question up in a new thread since this one is so long ;)
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RE: Repair, Don't Replace, Old Wood Windows

If the underlying lead paint is stable, a high quality latex paint carefully applied is adequate for encapsulating.

"N,inm,ayu cases"

A series of typos for 'Not in many cases.'

The keyboard has since been replaced.


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RE: Repair, Don't Replace, Old Wood Windows

I know this post is getting old... but I'm just discovering it! We have a 110 year-old brick bungalow in Tucson that we want to make liveable, and I would love to keep the old windows with the counterweights. I may try to do this myself, with a little help. They don't have to look new, just 'serviceable' as someone above said. Ideas??


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RE: Repair, Don't Replace, Old Wood Windows

Great advice, OP. I HATE vinyl windows and there is nothing better than a well-refurbished original window, with a storm window overtop if needed.

The original stained glass windows are all that are left in my home, unfortunately. but they sure are nice even just in finish and design of the window frame!!


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RE: Repair, Don't Replace, Old Wood Windows

According to me window repairing is a better option than window replacement; you can contact experts in window repairing field to solve your problem.

Here is a link that might be useful: window repairing


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