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Do I want low-SHGC windows on the east and west sides?

I live in sunny New Mexico and am doing research for having my ancient, awful aluminum windows replaced. I'm torn on the question of whether I want low solar heat gain coefficient (SHGC) windows, though. My house faces east-west with only two small, unshaded windows on the south side. Most of the windows are east or west, and these windows cause the house to gain undesirable amounts of solar heat in the summer, especially a large west-facing picture window which makes the living room really hot. Most of the east and west windows are fairly well shaded, but still let in a good bit of direct sunlight in the summer, especially in the afternoon. However, they also let in a lot of desirable solar heat in the winter when the sun is lower and gets under the shading more, especially a large sliding glass door on the east side which really helps to prime the house with heat in the morning.

So I don't know if I should be spending more for the fanciest LoE coating available for these east and west glazings. On one hand, it seems like it would help with summer overheating, but if it's going to block an equal amount of desirable winter solar gain, what's the point? Should I go with a less-serious LoE coating on the east and west windows? What about the south ones? There are only two; does it really matter much?

Asked by Nathaniel G
Posted Fri, 06/13/2014 - 17:10

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4 Answers

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Nathaniel,

The point is comfort. In your current situation you aren't comfortable when the sun is shining directly on the west facing picture window so why would you want to spend money on upgrading your windows and still be uncomfortable when the sun is shining directly on the window.

Using a high solar gain LowE coating on west facing windows is almost always a bad idea, even in cold climates, because while the free heat gain is great in winter it is a lot less great during summer and during the transition months.

High solar gain on east facing windows are a bit more ambiguous in part because a lot of people like the warmth of the early morning sun even when the weather is reasonably mild.

Per your thoughts on paying more for the "fanciest LoE coating", I am not sure what you mean.

LowE coatings come in high, moderate, and low solar gain varieties. Unless you are in Canada the low and moderate coatings are much more readily available from most window manufacturers. High solar gain coatings are often considered to be a specialty item and can be difficult to find depending on the window company.

Using a high solar gain coating on east/west facing windows will allow a high percentage of solar heat into the room and the coating will do (as designed) an excellent job of keeping that heat in the room, winter or summer.

Per the south windows, if the window company you are talking with offers high solar gain coatings then go for it - can't hurt.

Answered by Greg Smith
Posted Fri, 06/13/2014 - 18:53

2.
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Thank you for your answer, Greg. That all makes sense to me.

Answered by Nathaniel G
Posted Fri, 06/13/2014 - 18:58

3.
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Nathaniel,
Greg has given you good advice. For more information, you may want to see All About Glazing Options.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 06/14/2014 - 07:03

4.
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You are welcome, Nathaniel.

Thanks Martin.

Answered by Greg Smith
Posted Sat, 06/14/2014 - 22:00

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