Zone 5a - Marvin LoE 272 or LoE 366

Mrs_NyefnyefSeptember 27, 2013

I've been reading many threads on this forum about when it's better to use LoE 272 or LoE 366 glass, but the threads were about homes in Atlanta, Utah, California or the Southeast. I am in suburban Chicago, zone 5a. As the saying goes, "Chicago has two seasons, freezing cold and boiling hot".

I am replacing 5 windows in a 3rd floor (top floor) bedroom which faces SE. I will be getting Marvin Clad Ultimates. I got a few bids, and they all defaulted to the LoE 272 glass. Except one contractor, who said I would be better off with LoE 366. The price difference is not much between the two types of glass. Because this bedroom faces SE, it does get very warm on sunny days, but at the same time, the windows fill the entire wall so that at night it can be very cold.

In an older thread Skydawggy said "IMO 366 glass should only be used in a cooling dominated climate such as Texas, Florida etc." So should I tell the contractor who said I should get 366 glass, that I am going to go with 272, or should I be choosing the 366?

This post was edited by Mrs_Nyefnyef on Fri, Sep 27, 13 at 16:45

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For comparison --- 3.0mm - coating surface 2 / 1/2" airspace / 3.0mm clear glass IGU with 90% argon fill:

LoEó-366 - U.264, SHGC .274, VT 66%
LoEò-272 - U.272, SHGC .414, VT 72%

Center-of-glass only.

SHGC - solar heat gain coefficient
VT - visible light transmitted

IMO, you will probably prefer 366 in the summer and 272 in the winter.

    Bookmark   September 27, 2013 at 5:48PM
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Oberon - thanks for that info! But I still don't know which to choose for these 5 bedroom windows...

    Bookmark   September 27, 2013 at 6:02PM
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The U value is not much different between the two which is your defense against the cold. You will get much more protection against the heat in the summer but less visible light transmission in the winter with the 366. Which is more important to you? That should be the deciding factor.

    Bookmark   September 27, 2013 at 7:05PM
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I'd recommend the 272. The extra solar gain in the colder months can be a benefit. The 366 will provide a little bit more comfort in the summer, but the 272 should provide superior efficiency when all is said and done. I tend to agree with skydoggy.

    Bookmark   September 28, 2013 at 9:49AM
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Windows on Washington Ltd

Low-e 272 on the South facing windows.

You can use Low-e 366 on the other elevations.

    Bookmark   September 28, 2013 at 10:55AM
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Thanks for all the great advice. Another thing I thought about, especially in response to Eastbay10's message above, is that winter here lasts 8 months or so, versus a short summer. So winter considerations should have more weight in this decision and 272 glass would be better. On the other hand, I will say that even in the winter, that bedroom gets very warm on a sunny day, due to its unobstructed 3rd-floor SE exposure. So in that case, perhaps 366 glass would be better. Sigh.

I am concerned about the amount of tinting I might notice with the 366 glass. I love my view of trees and sky out these windows, and wouldn't want that altered or diminished. And, it should be noted that right now I have 1991 Pella Prolines with clear glass, rotting sashes and tons of draft. So new Marvin Ultimates with 272 glass would be such an enormous improvement. Relative to that degree of improvement, windows with 366 glass may only be a small margin better than 272 against the sun so as not to be noticeable except for more tint of my view. What do you think?

Any other advice or response to my thought process would be welcome.

This post was edited by Mrs_Nyefnyef on Sat, Sep 28, 13 at 13:31

    Bookmark   September 28, 2013 at 12:18PM
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In response to your latest message, I agree that 272 would be best for you. It will be considerably more efficient against heat than your current clear insulated windows and give you the winter benefits as well.

    Bookmark   September 28, 2013 at 7:59PM
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When looking at small samples of the different glass/coating types, the LoE coatings can look dark, but when you have them in an actual window in a home environment very few people really notice that there is a coating at all.

It's much more common for people to question if the window company forgot the coating since the homeowner was expecting to be able to see it - and they can't.

Since you live in a heating dominated climate, I agree with the previous posters that you will appreciate the advantage of higher solar heat gain in the 272 coating.

This post was edited by oberon on Sun, Sep 29, 13 at 9:00

    Bookmark   September 28, 2013 at 9:13PM
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Thanks everyone. This forum is great. LoE 272 it is!

    Bookmark   September 29, 2013 at 11:00AM
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Is the 272 better because she is SE, or should all windows be 272 regardless of direction? I am in Minnesota and read a previous gw thread where somebody said 366 is better for none south facing windows. I have no windows on the South side. So was curious what you guys thought.

    Bookmark   September 30, 2013 at 12:43AM
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Windows on Washington Ltd

272 would be better in her case because of the passive solar heating potential. Being in a heating degree dominated climate, you want to allow for as much of the free energy to enter the home through the windows in the winter months.

    Bookmark   September 30, 2013 at 6:05AM
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