Are you going to get replacement glass or replacement windows in total?

I talked to a couple of people about replacement windows for the group of 5 before, two Awnings over 3 casements and didn't like what I was hearing. So, I'm just looking to replace the glass now.

Current windows have a stained wood interior and trim as do all my interior moldings and base boards. The exterior of the windows are bronze clad.

What window brand are they? Are they old pozzi/jeld wen? It is usually best to have who supplied the windows replace the glass. If not, use a reputable glass company that can give you the proper information on what kind of Low E you're getting. I hope they're not old pozzi windows because they boot glazed their windows and you have to replace the sash to replace the glass.

The House was built in 89 and has Reuten Klein windows. Think they had already been bought out by another company by then and that company is out of business now, if I remember right.

I found two supposedly good companies on Angie's List but if I'm not just going to take whatever they want to give me I'm going to have to tell them what I want.

Efficientwindows.org tells me to get MSG or LSG glass with U value between .23 and .55, A SHGC of .25 to .4 and a VT of .5 to .6

How do I spec this glass?

Both local companies think Argon gas is a waste of $$ as it will be gone in a couple of years at most.

If you want those numbers you need argon. A good knowledgeable company should be able to source glass that has the requirements you desire. I think most replacement glass companies aren't use to dealing with customers that actually know what they want. Most just want another piece of glass to fill the hole. That being said you might need to do some digging to find the right people.

"If you want those numbers you need argon."

I see improved performance numbers by having LowE on surfaces 2 and 4, with the caveat that surface 4 may be more difficult to clean and have a more problematic dew point. Can't seem to find any info on doing surfaces 2 and 3 now, though I think that's what I have on my one Jeld Wen casement.

You won't find much information on IGU's being LowE coated on both surface 2 and 3 because it isn't done very often. In fact, it is very rare and I am not aware of any major company that even offers it.

The primary problem with coating both surfaces inside an IG is heat gain. Heat can get in (between the lites) but it can't get out, and either the seal fails, or the glass breaks, or both.

One way to minimize glass breakage in that situation would be to heat strengthen both lites in the IGU, but that doesn't affect potential seal failure and it is an added expense.

Potential energy advantages to coating surface 2 and 3 are minimal and are easily outweighed by the potential disadvantges including both higher cost and the increased potential for failure.

Is the replacement a Jeld Wen wood window or vinyl window?

I ask because if you have a Jeld Wen wood window then the IG was manufactured by Cardinal. If you have vinyl then the IG may have been made by Cardinal, or it may have been made in the window factory. If from the window factory then it could be any one of several IG systems that Jeld Wen vinyl windows use.

If you have NEAT coating then the glass came from Cardinal. If you have a Cardinal IG in your window then you almost certainly don't have both surfaces 2 and 3 coated.

I would strongly recommend that you reconsider the idea of surface 2 and 3 coating and look at surface 2 and 4 if you want the improved U value performance or look at surface 3 with a high solar gain coating if you want to maximize solar gain.

Regarding sungate 500, if you were to choose a surface 3 coating alone you would have U.31, SHGC .72, VT .76.

However, if you were to choose (and someone agreed to fabricate) surface 2 and 3 coated, you would be looking at U.28, SHGC .63, VT .70.

Dual coating would result in an improvement in U value but a much more definite loss in solar heat gain and visible transmittance.

Keeping in mind these are glass-only figures (3mm glass, 1/2" airspace, 90% argon fill) and that the sash/frame used has a significant influence on final numbers.

Just out of curiousity, why do you think your windows are coated on both 2&3?

This post was edited by oberon on Wed, Aug 14, 13 at 14:14

Bluebaru,

The surface 4 coatings that are out now are not harder to clean.

The Dew point and condensation concerns are definitely valid though.

If you run high humidity, be wary of surface 4 coatings.

+1 WoW. You hit it right on the head -- if someone is using a surface 4 coating then attention to indoor humidity is extremely important.

Surface 4 coatings are interesting for a couple reasons.

First, despite the fact that center-of-glass temperature is going to be about 9°F colder (assuming delta T of outside 0°, inside 70°) than the same IG without the coating, a person standing in front of the window is actually going to feel warmer than they would standing in front of a window without the surface 4 coating because the coating is reflecting heat back into the room; the same heat that would have increased the glass temperature 9° if the coating wasn't there.

Second, keeping the same indoor/outdoor temperature difference from the previous paragraph, then the edge-of-glass (outer 2 1/2") will be only 3°F colder than would be the same IGU without the surface 4 coating.

While the temperature does drop at the edge-of-glass, it drops three times less in the area most likely to have condensation issues than it does in the area (center-of-glass) that doesn't normally see condensation.

Dew point is based on the amount of moisture in the air. Dew point is unrelated to the temperature of the air.
Of course if the temperature of the air (or any object) drops below the dew point you have condensation. Above dew point you have evaporation. Simply nature trying to keep things balanced.

So imagine a home at 70°F and 40% relative humidity. In that scenario the dew point is 43°F - what's the window doing?

If it's 0°F outside a clear glass double pane window (no coating, 90% argon fill) will have a center-of-glass temperature of 43° - right at the dew point. Of course edge-of-glass will be colder. Condensation at the edges is almost a given unless steps are taken to avoid it. Center-of-glass condensation is possible.

The same dual pane with a surface 2 or 3 soft coat will have CoG temperature of ~54°-56° depending on the coated surface and the coating used, and ~39°-42° EoG temperature depending on which "warm-edge" spacer used. Edge temperature using aluminum would be a good bit lower than 39°F

Again keeping in mind that we are considering a delta T of 70° in that scenario and 40% RH, which is really high when it's that cold outside.

Lower the indoor RH to 35%, what happens?

That depends on whether the RH was lowered by increasing indoor temperature to 75° - which will lower the RH to 35%, but will not affect the dew point - it remains at 43° - or, leaving the air temperature at 70°, but removing moisture from the air by using exhaust fans, etc. - enough to take the RH to 35% - lowers the dew point to 39°F, which leaves both CoG and EoG temperatures above or right at the dew point.

So we add the surface 4 coating and lower the CoG temperature to ~45°-47°, still well above dew point.

Edge-of-glass temperture drops 3° to ~36°-39°- which is in the range of developing edge condensation.

Dropping RH to 30% (by removing moisture) and dew point drops to 35° which is below the edge temperature of the IG with the surface 4 coating when using a low conductance spacer.

Some folks might complain that 30% RH is too low or may ask what happens when the outdoor temperature drops to -10°F or colder yet?

In those cases one might ask "how many days a year does the delta T exceed 70°?". if the answer is more than a handful, then one might very strongly suggest that a triple pane with two LowE coatings and argon or even krypton fill would be a much more realistic option.

But, in a milder climate where 0°F or colder is relatively rare, occuring only a few times a year, then the benefit of the surface 4 coating with the right spacer in the IGU is definitely worth considering, because the potential for increased condensation really is only a matter of being careful about how much moisture is pumped into the air in the home during those few really cold days.

This post was edited by oberon on Wed, Aug 14, 13 at 18:30

Great information as always big guy.

That is a neat tidbit on the edge of glass vs. center of glass temp drop with surface 4.

"You won't find much information on IGU's being LowE coated on both surface 2 and 3 because it isn't done very often."

I may be mistaken on that, it may be 2 and 4 I got. After more research it looks like thats the way to go, with the possible exception of E2 on surface 2
Current plan is to get a MSG IGU, with the coating on surface 2 and I am looking into i89 for surface 4 but don't think the local people want to deal with Cardinal glass, SO, a good alternative suggestion for surface 4 would be nice.

"Is the replacement a Jeld Wen wood window or vinyl window?"

The only Jeld Wen I have is a wood, aluminum clad, casement pair, in a room addition that was added 3 yrs ago. All the windows I need to replace the glass in are RK's, also Aluminum clad wood.casements.

The IGU's are 5/8" with both glass panels being 3/32", so I have a 7/16" air space. I've been informed most of the local available glass is 1/8" so I guess that's one more issue. Maybe they can use the 1/8" and just cut the air space down to 3/8".

Thanks, WoW.

That little variation between CoG and EoG is pretty significant in my opinion, so it would be nice if the information was more available.

Bluebaru,

The surface 4 coatings have only been around for a relatively short time, just a couple of years.

It is possible that your original windows were coated 2 and 3, but my point was you wouldn't be likely to find that combination today, and even if you could, it really isn't a very good idea anyway.

Single strength, or 3/32" or 2.2mm glass is out there, but as you have found that double strength, or 1/8" or 3.0mm glass is becoming pretty common.

As you said, going with 1/8" / 3/8" airspace / 1/8" is an option for sure.