Low-E windows a mistake in the north?


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Old 02-26-06, 06:53 PM
HomeBody2U
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Low-E windows a mistake in the north?

Four years ago I had a bunch of leaky, warped 1950-ish wood windows replaced with Alside UltraMax double-pane vinyl replacement windows. They fit nice and tight and I like everything about them except for one thing: On bright, sunny winter days you can stand in front of the windows -- even on the south side of the house -- and you still feel COLD!! There is none of the warmth that I used to enjoy with my old windows.

I'm starting to wonder if I made a mistake by choosing the Low-E glass option up here in western NY. There's not really that much sun on my house, even in the summer, but on the rare winter day when it's clear it would sure be nice to get some "free" heat from the sun. Ideas, anyone? Thanks.
 
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Old 02-26-06, 07:06 PM
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Cold Windows

Here's some statistics that are true of all windows, including Alside. If it's 0° outside and 70° inside, the resulting center of glass temperature is about as follows:

Single glass 14-17°
Clear IG 44°
Single with storm (your old windows?) 45°
Low E glass with argon gas 57°

Not only is the glass more energy efficient, but presumably the windows are a lot more airtight than the old drafty ones.

I'm not sure why it would seem colder now than in the past. Perhaps the house is not well insulated, perhaps drafty in other areas, or the windows are poorly installed and therefore drafty, or maybe you're just more aware of cold that you do have because now you have energy effient windows. Low E does filter out some of the sun's solar heat gain, so you don't feel the extreme heat you would have with uncoated glass, but in your area the benefits of Low E (resistence to cold, condensation, etc) outweigh the reduction in solar heat gain.
 
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Old 02-28-06, 04:51 AM
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Question for Tru_Blu

I'm going to be installing double paned vinyl replacement windows, non-low E and not argon filled. What would glass temperature be for this configuration?

BTW, where did you get your glass temperature numbers from?

Thanks,

Dave
 
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Old 03-01-06, 09:25 AM
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Glass temperatures

For a vinyl window as you described, without Low E, without argon gas, the resulting center-of-glass temperature would be 44° (The same "clear IG" temperature I mentioned earlier). Actually it can vary by a degree or so depending on the glass thickness. In northern climates it's pretty easy to get condensation on clear insulating glass without the Low E, but there are still people getting them that way.

Please note that the edge of glass temperature is colder than the center of glass. Although the center temperature is in the 40s the edge temperature can be as low as in the 20s. The edge temperature is largely dependent on which type of spacer material is used between the glass. Also keep in mind that those stats are based on 0° outside and 70° inside, which for some climates is not applicable.

I originally got those statistics from Cardinal glass (one of the largest glass manufactures in the world). However I've repeatedly seen the same performance statistics from numerous window manufacturers, seminars, and articles over the years. I've accumulated quite a stash of resource materials in my 28-1/2 years of being in the business ;-)
 
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Old 03-01-06, 09:43 AM
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The figures I have from Libbey-Owens-Ford are based on identical criteria and are very similar:

17F for single pane
45F for clear IGU
53F for Low E
55F for Low E w/argon

these values will change depending on the size of the IGU and type of spacer used.

The u-value of a clear glass IGU (.49 ave) would be very poor in comparison to a low-e IGU (.34 ave) or a low-e w/argon IGU (.29 ave) The difference in u-value directly affects the wintertime temperature of the glass, which is what most people are concerned about in a heating climate.
 
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Old 03-01-06, 12:02 PM
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Glass Numbers

Thanks Tru_blu and XSleeper.

Based on what you guys have said, it seems that the low-e option gives a pretty good bang/buck and is probably worth getting when I order my replacements.

Dave
 
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Old 03-01-06, 02:41 PM
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Low E

Definately! I'm so glad you're now leaning toward Low E instead of clear IG. It really really is worth it!
 
 

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