Insulated curtains & Low-e / Argon windows

Old 02-06-09, 09:36 AM
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Insulated curtains & Low-e / Argon windows

I have recently heard that it is not advisable to use insulated curtains to cover low-e windows. I also heard that solar shades are recommended in the summer (for low-e) to reflect the light back out the window. It's a little confusing so I was hoping to get a little more info from this forum. Thx all...
Old 02-06-09, 10:21 AM
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It's not that you can't or shouldn't hang insulated curtains (I've never heard that before), it's that you don't need to. You can hang pretty much whatever you want to, tho.
Solar shades are not needed either unless you want them. The thing you need to be careful about, is mounting any window treatment, as the glass is very fragile and you could easily break the glass.
Old 02-06-09, 10:33 AM
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Never heard that before either. Most new double pane windows say never put any films on the interior glass, but never heard of any window treatment issues.

LoE glass helps prevent Solar heat gain from sunlight streaming in the window in the summer, and helps prevent heat loss from the interior in the winter. Trying to "reflect" heat back out in the summer wouldn't be very efficient. Solar exterior coverings or awnings would of course be effective, since it would prevent the sun from ever reaching the window.
Old 02-06-09, 11:39 AM
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In a cold climate, insulated curtains can block the heat and still allow warm air to circulate over the inside of the glass. The now colder window becomes more susceptible to condensation and ice. The thinking may be to let the window insulate by itself to avoid moisture damage. Window quilts avoid this by being sealed around the edges, thus no flow of warm air to contact the window.

As for solar shades, I had to Google them to see what they are offering. Although they talk about “technology” the pages I reviewed were lacking in any emissivity/reflectivity numbers or other characteristics that would indicate they are anything more than a shade that allows enough light through so you can still see what is outside. A quote from one manufacturer “Our premium series has an approximate openness of 5%, UV blockage of 95%,” . Yes, if you block 95% of the light coming through you will be blocking 95% of the UV. Perhaps there is more to them than I found, like a special reflective material to actually send the solar energy back out through the window, but lacking any real technology, they appear to be simply shades you can see through. To be fair, I see nothing really wrong with them. They will absorb a certain amount of solar heat and that heat will be radiated in all directions, thus about half will be sent back outside, but in turn they will be blocking the IR from leaving the room in the same manner. Installed outside I like them especially down south, inside, they appear to be just partial shades, which I guess is ok. IMO

Old 02-06-09, 04:05 PM
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Oberon could answer this question if he'd pop his head in here... but I have heard of such a problem, and it has to do with the reflected light bouncing off the low-e coating and causing heat buildup inside the insulating glass unit, or IGU. If the heat buildup inside the IGU becomes too great, it may result in broken glass or a seal failure.

Depending on the type and placement of the low-e coatings, a percentage of heat is reflected back to it's source. So heat that is attempting to leave the home is reflected back toward the home. If you put reflective shades on the inside of the home, you could potentially be creating a problem. Whether or not there is any truth to it, I don't know... but I have heard about this at window dealer's meetings. How much of the hype is from manufacturers who just want to blame their seal failures on something is a good question.
Old 02-08-09, 06:10 PM
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XSleeper is exactly correct. You never want to trap air between your shades/blinds/drapes and an IG window with a LowE coating. To do so, you are risking damage to the IG up to glass breakage in the right circumstances.

Glass/IG/LowE manufacturers will recommend that if insulated shades, drapes, etc. are used then there should be at least a 2" air gap between the glass surface and at least a 1-1/2" gap between at the top and bottom in order to allow air circulation between the glass and the material.

Installing an interior solar reflective shade over a LowE window is likely to be a very bad idea. You are realy risking the possibility of trapping enough heat to casue problems.

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