Good morning tulips and welcome to the North country where it has been chilly for the past couple of weeks.

As the temperature goes down, condensation and ice on the interior of windows does become more likely - particularly in the case of older window units. And, since it is currently -21F here this morning (NW Wisconsin), I imagine that your temps are similar or even a bit lower than are mine, depending on where in Minnesota you call home.

Okay, on to condensation and ice on the interiors...

I have posted versions of this reply on this forum (and others) in the past, and hopefully it may give you an idea of what is happening with your windows. It's long and a bit involved, but then my posts usually are!

Okay, the reason why there is condensation or frost or ice on the interior of your window or storm window is because the surface temperature of at least part of the window is below the dew point temperature of the air in your homethatÂs itÂa very simple explanation.

Unfortunately, the explanation as to why the surface temperature of your window (glass) is below the dew point temperature of the air in your home may be a bit more complex  so I am going to offer a few thoughts and maybe even throw in a few numbers that I hope might help your situation.

In the summer, when you pull something cold and refreshing out of the refrigerator, and the air is warm and humid, that cold and refreshing beverage container suddenly and quite magically becomes instantly wet  just as soon as it is exposed to the air. What has happened is that the temperature of the container fresh from the refrigerator is below the dew point temperature of the air  which has caused condensation on the outside of that container.

What happens to your windows in the fall and winter is that the surface of the glass is below the dew point temperature of the air in your home  which is causing condensation on the surface of that glass.

Dew point is defined as saturation vapor density...or put in simpler terms, when the air reaches 100% relative humidity and can hold no more moisture.

Relative humidity is, well, relative.

Relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature. Put a bit more simply, dew point is 100% relative humidity or the point where the air - at that temperature - is no longer able to hold any more moisture. If the air has reached vapor saturation (100% relative humidity), then the air will release moisture...be it on the outside of that cold beverage container in the summer time, or be it on the interior glass surface of your windows in the winter time, it makes no difference. If the surface temperature happens to be below freezing, then that moisture becomes frost or even ice.

In order to stop condensation from forming on the surface of a window, you either have to lower the dew point temperature of the air in your home to a level below the dew point temperature of the window surface, or you have to warm up the window surface to a temperature above the dew point temperature of your home, or a combination of both.

Lowering the relative humidity of the air in your home may have absolutely no effect on controlling window condensation or it may completely solve your problem  depends on how you lower the relative humidity and what affect the "how" has on both the moisture level of your air and the temperature of your windows. All this because there are two ways to lower relative humidity  first, you can increase the air temperature in your home or second, you can decrease the moisture content of the air in your home.

By increasing the air temperature in your home you will lower the relative humidity but you will not change the dew point  which is based on the amount of water vapor in the air and is not based on the temperature of the air. So, while the RH is lower with higher air temperature, it may not effect condensation on window surfaces at all  unless the rise in air temperature also caused a corresponding rise in window glass temperature to a level above the dew point temperature.

But, lowering the amount of water vapor or moisture in your air will lower the dew point temperature as well. And if it lowers the dew point temperature sufficiently to drop it below the temperature of your window glass  no more condensation issues.

The amount of moisture in the air is measured in grams per cubic meter, which is kind of nice for our metric folks but not so nice for our non-metric folks; but the metric version is much easier on the calculator than the English version. However, in the interest of making this stuff easier to understand for all of us non-metric types, I am going to use Fahrenheit rather than Celsius temperatures in the calculations.

Okay  consider your home at 65 degrees F and with a relative humidity reading of 40%. There are 6.25 grams of water in a cubic meter of air in your home in that particular scenario - which then equates to a dew point temperature of 38 degrees F. So at 38 degrees the air will be at 100% relative humidity or at saturation vapor density.

Now, if your neighbor keeps her house at 75 degrees, but she also has 6.25 grams of water per cubic meter in her air, then the relative humidity in her home is 29% - versus your 40%. But, and hereÂs the kicker, the dew point temperature in her home is still 38 degrees.

While the relative humidity in her home is much lower than is the relative humidity in yours; if the surface temperature of the windows in her home is 35 degrees she will have condensation on those windowsÂyet if the surface temperature of your windows is 40 degrees  only five degrees warmer  you will not have condensation on your windows.

So, while her handy humidity gauge reads (correctly) only 29% RH Â she has a condensation problem.
While your handy humidity gauge reads (correctly) 40% RH Â you donÂt have a condensation problemÂSWEETÂwell, for you anyway, not her.

If your home hygrometer measures the relative humidity in your home at 60% while the temperature of your home is 70 degrees, you will have a dew point temperature of about 51 degrees  meaning that if the temperature of the window surface is below 51 degrees then you will have condensation - so now we talk a little more specifically about windows.

The interior surface temperature of a single lite of glass, when the temperature outside is 0 degrees F and the inside air temperature is 70 degrees, will be about 16 degrees.

Add a storm window on the outside and the surface temperature of the inside lite jumps up to about 43 degrees  a huge improvement.

But these are center-of-glass readings and not the temperature readings at the edge of the window where condensation usually forms. A typical clear glass dual pane window is going to have center-of-glass temperature reading pretty much the same as a single pane with a storm  something that is often claimed (correctly) by folks who advocate refurbishing windows rather than replacing (something that I am not going into here  I am NOT advocating either replacement or restoration in this post. It is long enough and detailed enough already without opening that particular can-of-worms!)Â
However, if that dual pane has a LowE coating and an argon gas infill then the center-of-glass temperature will be about 57 degrees  a 14 degree improvement over a clear glass dual pane or a single pane with storm window  but again, and more importantly, there will be a comparable edge of glass improvement as well, particularly if the IGU (Insulating Glass Unit) was manufactured using a warm edge spacer system. Also, the dual pane is going to have desiccant between the glass layers. Desiccant absorbs moisture keeping the inside of the dual pane system very dry.

The advantage? If it gets cold enough outside, the temperature in the airspace between the lites can get very low. By keeping that space dry, it helps to keep the dew point temperature very low as well; something not always possible when using a single pane and storm window.

Oddly enough, a single pane with a good and tight frame and sash assembly may be more prone to condensation than will a less tight single pane window simply because air (and moisture) will leak out of the looser window while the tighter window may be more likely to trap the moisture inside the home. And, while a tight storm window can help the interior lite to avoid condensation (when compared with a single lite and no storm), the storm window itself may frost up when the temperature is low enough  at a temperature usually well above the temperature that will cause the dual pane to ice up. It is unavoidable given the right circumstances

So what does a window temperature of 57 degrees mean? Well, as I mentioned earlier a home kept at 70 degrees with a 60% relative humidity has a dew point temperature of 51 degrees so it is much less likely that there will be condensation problem on those particular windows than there would be with a less energy efficient window - despite the relatively high relative humidity in the home.

But, there is always a "but"Â

Again, that 57 degree glass temperature is still a center-of-glass reading and the edge of glass temperature will be lower - actual temperature is dependent on both the spacer system used in the IG unit construction and on the material used to construct the sash. So even with a "57 degree" center-of-glass temperature it is still possible to get window condensation if there is enough moisture in the air.

And consider that the interior glass temperatures are based on the fact that moving, warmer, indoor air is actually in contact with the glass at a given time. Curtains, shades, other obstructions can cause problems by blocking airflow across the glass  airflow that can have a huge effect on the condition of the window relating to condensation. Also, bay and bow windows can be more prone to condensation  again because of the possibility of decreased airflow over the glass.

And finally, what can happen to the dew point if you keep your home at 70 degrees and you have a 65% relative humidity? Well, for one thing the dew point has jumped up to 57 degrees which we have already noted is the same as the window temperature. For another thing, anyone with 65% relative humidity in a home at 70 degrees has way too much moisture in their air and they are in serious need of some sort of ventilation system  or at least several good exhaust fans!

Dear Oberon...

Many thanks for the information. I am printing it out to show my husband. Keep warm - it's -20 degrees F here just North of MPLS.

Previous answer excellent. If these windows may be MARVIN INTEGRITY ( would be replacements ) contact Marvin directly. They had a seal problem and agreed immediately to replace seals on thirty double hung windows when I called after five years. I know this probably does not help you but maybe others. It is only minus seven in michigan and no you never relly get used to it even if you grew up here. Good luck.

You are welcome tulips. And if you have any more questions please feel free to ask anytime.

I have heard we may get above zero tomorrow? Today almost made it...at least it was minus single digits for the high rather than minus double digits for the high!

bigfoot,

Just curious, but what was the actual problem with your windows? You mention seal failure, but was that glass (IG) seal failure or something else?

As I said, just curious.

Thanks!

Wow, that was a really informative and helpful post!

I just logged in and took a look at this message because we are looking at replacing two Milguard aluminum dual pane windows in our bathrooms that are always wet in the morning (live in Northern California, so temperature is less of a culprit, but we do have very high humidity in the house).
We use a dehumidifier, and that does help some.

So I have a couple of questions:

1) Are Milguard vinyl dual pane windows with Argon and low-e (no sun on these windows, Northern exposure) likely to help us? (indoor humidity 65, indoor temp 68, outdoor temp usually 30-40 in the morning)

2) What would a good ventilation system be for our house (we are near the base of a range of hills/mountains, and crawl spaces in our neighborhood tend to be moist year round, hence the high indoor humidity).

Thanks

Hi Davepw,

Ye, the windows you describe should help. But, getting some of that moisture out of the home will help a lot more.

I am far from an authority on ventilation systems...I know that there are folks who post in THS who are experts in that area. You might try posting your question in the Heating and Air Conditioning forum as well.

Good luck

Thanks, I'll plan to formulate a question on ventilation and post to the HVAC forum. Our house is half remodeled (insulated, new vents, etc) and half old construction. The furnace is located at the end with the new construction, heat does not make it to the bathrooms and bedrooms very well. Coupled with the insulation issues, the air in the bathrooms is colder and more humid. I think we probably need to force more heat into the old part of the house, and get the air circulating better. Better bathroom windows will treat the symptom, but not the problem. Probably need to do both!

It has been cold here Obi-One. Working outside in the Twin-Cities has been bad on my old body!!! Even my stellar and fit 23 year old son has voiced his unhappiness on this weather we've seen here in MN. I can't remember the last time we've had such a cold stretch. I'm thinking my high school days around 76 is the last time I had to deal with this stuff. One thing it's done more than anything is show people how bad their windows are leaking. I can handle the one week stretch but we're going on the fourth. When our highs are in the negatives it really gets in the bones!!! Stay warm & great post above, as you always do!

The storm windows in a 3 window bay area in our master bath are usually frozen during the winter months - we live in the upper midwest. (The storms are aluminum I think and the inside windows are double hung wooden and are about 18 years old). This is a 2nd floor bathroom with two exhaust vents that are used regularly so there is no condensation on the inside windows, only the exterior storms. If I'm understanding all the helpful prior postings on this topic, my problem is with the interior windows needing weatherstripping to prevent warm air escaping to the storms. This is probably a dumb question, can you tell me what area of the inside window needs weatherstriping? Also I have never been able to understand why on the 1st floor right below where we have a similar 3 window configuration (and the windows are the same age), we never have frozen condensation on the storms. Any thoughts?
I tried to post a picture of the windows but I can't figure out how to do it???

Hey Guy!

You are right about that one and I know that this can't be a great time to be replacing windows - that is a given - way to freakin cold for that!

Although today wasn't bad...+14 and sunny - T-shirt weather around these parts this year.

Hi Joan,

Yep, you have warm air and moisture escaping thru the inner windows and affecting the storms.

First thing is to check and see if the storms have weep holes that are designed to let some of that condensation escape. The weep holes can be quite small (or large on older wood storms). If you find them and they are plugged or closed in some way, open them and that will help.

Second, it certainly wouldn't hurt to check the weatherstipping on the interior windows - I assume that these are operating units and not fixed units? Preventing as much air as possible from going out your windows is certainly a good idea. Where the windows may need improvement is dependent on the type of window.

The downstairs windows probably avoid the icing because the interior windows are tighter or the storms may have weep holes that are working. Also, warm air does rise and it does carry moisture so there may simply be more moisture upstairs as well.

Joan, Do you open this window during the Winter or is it locked during the cold months?

What I see most the times in this scenario is the homeowner using this window to ventilate the bathroom moisture after a bath or shower. By cracking the window with the vent fans on the air clears out much faster. The mistake they make most of the time is forgetting to lock the window after their done using it. Since most window locks are on an eccentric of some kind or a hooking device. This pulls the sash tight into the opening and tight to all the weather seals. If the lock is left undone the interior air will find any tiny crack and flow outward. So make sure the sashes are locked.

If your window is locked then the game changes. The reason most bathroom windows seem to generate leaks more often is the sashes of these windows see a lot more moisture than any others in the home. With all this moisture on these sashes they tend to warp or twist as the years go by, at least this is what I've found over the past two decades. Here in the Upper Midwest our windows are subject to much more of the elements. Here in MN for example our windows are seeing 100 degree Summer heat to -20 in the Winter. I know how it affects my body, so you can imagine what a wooden window endures. Usually during my inspection I see the sash has a simple twist in it which has pulled it off the weather stripping and allowed it to leak. You can adjust the weather stripping to correct the problem very easily. The easiest way to see where it's blowing out is with an incense stick of some kind. Just light it up until you have a good stream of smoke and go around the window. Depending on the barometric pressure that day the smoke may blow in or out. You just have to watch carefully. You could also kick your furnace up to cause a positive air flow inside the home. This will almost positively push the smoke outside. Just follow along the seams of the sashes and it should point itself out quickly. Then you'll know where to at least start the corrections. Good Luck!!!

Thank you for your responses. I'll look for the weep holes. No, I never open these windows in the winter, so they are always locked tight. We regularly use our vents during and after showers to vent to steam and they work reasonably well or at least I thought so because of the lack of condensation on the inside windows.
I'll try the idea of incense. Also, if I can figure out how to swap the downstairs inside windows with the 2nd floor ones right above where I have the frozen storm condensation, that might be interesting to see if my problem goes away.

Ice, condensation and seal failure are just a few of the features and benefits derived from the metal spacer systems.

When you shop for replacement windows, be sure to consider the alternate to metal spacers, Super Spacer.

Michael

The argument that one spacer system is inherently superior to another or all others is ripe with the possibility of misinformation, misunderstanding, and certainly a great deal of emotionalism.

Each system has its proponents and its detractors.

In the past, polysulfides, silicones, butyls, and other sealant or adhesive materials were used as the primary (and often only) seal for many aluminum spacer systems up to the advent of the original warm-edge spacer systems. Many of these same aluminum spacer systems have shown extensive seal failures when analyzed possibly as high as 6% - 10% seal failure rate at 10 years for some of these units.

Virtually all newer spacer systems, including SuperSpacer, use a dual seal system which in the case of the SuperSpacer system includes, primarily, a hot-melt butyl sealant as the primary moisture or gas seal and an acrylic-adhesive as the primary structural seal.

Unlike other systems, however, SuperSpacer is "reversed" in that it places the structural seal inside the IGU (between the lites) and the primary or moisture seal to the exterior of the structural seal. Does reversing the moisture / structural seals (compared with other systems) make SS an inferior product? No, not in the least actually SS outperforms every other system on the market, including TPS, in energy performance numbers
given that Super Spacer is generally only about ½ to one degree better than TPS at the edge.

The hot melt butyl primary seal used with the SuperSpacer system has a very specific application temperature range of 275º 325º. If the applied material is outside of this range, then the P1 chamber testing can be significantly reduced to as little as two to three weeks to seal failure. What happens in the field in this case?

In addition, SuperSpacer allows the use of polysulfides, polyurethanes, and even silicone as the primary moisture seal. The problem is that none of those options is impervious to air and air/moisture intrusion into the airspace may be a possibility with the use of those materials.

Edge Tech advertises that their system goes 80+ weeks in a P1 test. They advertise that the "metal" (stainless Steel) systems go 40+ weeks in the P1 chamber in the same marketing brochure Edge Tech also made the claim that none of the other systems tested lasted more 40 weeks. What they dont explain is that the "40+ weeks" of the metallic system was actually 80 weeks for a PIB / silicone dual seal spacer system.

Some industry folks suggest that one week in a P1 chamber is equal to one year in the field while other folks suggest that one week in a P1 chamber equals one week in a P1 chamber - and nothing else should be inferred. However, after 80 weeks or so in the P1 chamber the bond between the glass and the seal begins to break down possibly as much from glass deterioration as from spacer material failure.

Am I slamming SuperSpacer? Again, not at all.

When manufactured to strict quality control standards and exactly as specified by the manufacturer, then SuperSpacer really is a very good, even superior, product.

What Edge Tech does really well is market their product(s). They have what appears to be an excellent, even superior, product; but they also have a marketing program that totally kicks butt. They have opened areas of discussion that really didnt exist prior to their introduction of itthey have emphasized SSs inherent advantages while ignoring any potential disadvantages (which is what marketing folks do, of course). They have invented new ways to categorize window spacer systems in some ways they have introduced the idea of IGU spacers to the general public.

Energy performance and durability are what these things are ultimately about. How do they compare?

At the edge of the IG, SuperSpacer is the best performer with TPS (Thermoplastic Spacer) second by about a degree or so. Cardinal Glasss XL stainless steel system (there are a couple of different ones on the market, but Cardinal is the largest manufacturer) is about two degrees or so lower than TPS a bit better than Swiggle. Drop another degree or so to Intercept and about another 6º to 8º for aluminum.

Ultimately, using a LowE coating will have a much greater effect on the overall unit temperature performance than does the choice of which one of the "warm edge" systems.

Of course using a LowE coating with SuperSpacer and with Swiggle still keeps SS a couple of degrees warmer at the edge, but these are also ratings of the "raw" IGU so what happens when the unit is in a frame? Well, how about this for thought from a joint Canadian and European study on the performance of various edge systems:

"Conclusion

The thermal resistance of the spacer bar material influences the glass temperature at the edge-of-glass region of an IG unit. Based on the limited testing performed at IRC and computer modeling at EMPA Switzerland, the spacer bar with the highest thermal resistance shows the warmest glass temperature on the warm side and the coldest temperature on the cold side of the glass at a distance 5 to 60 mm from the edge of the IG unit. But the effect of the type of spacer bar on the overall thermal resistance (and tote heat loss) through windows depends heavily on the window design and material. Therefore, the full impact of thermal characteristics of the spacer bar material on the thermal resistance and the condensation resistance of a window should only be determined by testing complete window assemblies."

Heck of a concept testing complete systems rather than independent component testing to determine how the system will perform.

Durability some folks will suggest the idea that desiccant is used in most spacer systems in order to hide seal failure.

While it is correct that the desiccant used in these systems could absorb moisture in an IGU so that for many years there would be no evidence of a seal failure, a catastrophic seal failure, like those seen in some older single-seal, organic-seal, IGUs would overwhelm the desiccant relatively quickly and could cause the window to fog as well but this is much less likely with todays dual seal systems be they non-metallic, metallic, or otherwise.

But what if there is a seal failure?
Well, the desiccant used in these systems (except TPS which includes only 4% desiccant in its structure) could very well prevent moisture from forming inside the IGU for many years even with a minor seal leak and to play devils advocate, so what?

Well, if the window was argon filled (which is true of half of IGUs manufactured today), then the argon will escape possibly to be replaced with air. But, if only half of IGUs today have argon fill then what about a window with no argon that has a "leak" as noted what happens to the energy performance?

Basically nothing.

There is virtually no difference in the energy performance numbers of an IG unit sealed or unsealed. If the desiccant was sufficient to maintain the interior without condensation, then the LowE coating would be safe as well.

As I said though, I am playing devils advocate and real world numbers as well as lab testing are very specific that seal failure numbers in newer systems are extremely low.

Kommerling TPS claims that they have never had a failure. EdgeTech claims less than 1% over 20 years and Cardinal advertises less than a quarter of a percent using XL for 20 years.

Swiggle is higher, Intercept is much higher. Depending on the source of the information, Intercept may be as high as 6% (or more) at 10 years failure rate. This is primarily a manufacturer rather than a product issue, but it has become a very serious problem for several major window companies.

And speaking of argon, filling an IGU to 100% with argon will improve performance by 16%. 50% argon fill improves performance by 8%. 25% argon fill improves performance by 4%. Notice the trend?

When manufactured to strict quality control standards and exactly as specified by the manufacturer, then SuperSpacer really is a very good, even superior, product.

I agree! That is why we use it. Our products are fabricated with IG units made in a plant built by and supervised by edgetech.

I'll submit some pictures soon of some XYZ windows, about 9 years old, suffering from frost, seal failure and ugly stained wood..all with the infamous metal spacer.

We are replacing 550 of them in an adult living center. You're reading that right..550 windows in one complex with seal failure, ice buildup at bottom edges, rotted bottom sash rails, rotted sills, etc.

Michael

Curious - whose windows are being replaced?

Hmmmmmmmmmmm...I think I must be careful so I'm not shipped off to disney world.

Don't get me wrong. I love the metal spacer windows. They are keeping us extremely busy, especially this time of year when frost and ice grow on the sash edges.:)

I spent 8 days at the home and garden show talking to prospects about health smart windows. I'll be very, very busy as a result of that.

Michael

Disney?

MARVIN INTEGRITY problem was a weatherstrip seal in the side tracks. It was not a glass seal problem.

Thanks bigfoot - I appreciate the reply!

To complete the answer the original issue with MARVIN windows was condensation on glass and in side tracks on lower left and right of bottom sash. When windows were raised mildew and mold could be seen in side tracks. If window was opened in winter ice buildup was evident in area from moist air from in and cold air from out in lower corners. Entire side weatherstrip seals appeared shrunken even when new and did not touch sill on exterior. Small foam blocks applied on exterior at this sill/weatherstrip area did not begin to seal the gaps. Side weatherstrips appeared undersize considering the size of windows. This is a tilt in to wash window and obviously you have to be carefull on the seals when you do this. This was a new house in 2001 and I think a lot of moisture came from basement concrete and walls as it slowly cured. I also have a large aquarium that can easily evaporate six quarts of water per day if not covered well. Ended up taping side seals on windows and it significantly cut down on drafts. Also noticed inside of clear tape was covered with dust showing just how bad the problem was and condensation on lower glass area of both upper and lower sash was virtually eliminated. Hopefully the redesigned side seals take care of this in the spring. Nice wood window on the inside with fiberglass exterior. Large glass area with a fairly narrow frame around it .