Reduce heat loss by up to 75% using cellular shades
Yet another day of near record cold here and I realized that most of the winter I’ve been neglecting one of the simplest things I could be doing to warm my rooms – closing the curtains!
Yes it’s true – even The Energy Geek forgets the basics.
Why is closing the curtains so important? That little air gap between the window and curtains acts as insulation and can cut the heat loss out your windows by half or more. This is pretty significant when you consider that the windows may be sucking more heat out of the room than the walls.
Another reason you want to close the curtains is to reduce drafts. When the warm room in the air gets near the window, it cools down. Cool air is more dense (i.e. heavier) than warm air so it drops down to the floor. That creates a void of less dense air which other air in the room rushes in to fill. Voila! A convection current forms and you feel a draft.
An even more esoteric reason for closing the curtains is something called radiant heat loss. In the same way that you feel warm when the sun hits your skin (the sun is radiating energy that your skin absorbs), the process works in reverse when it’s cold outside. Your warm skin radiates heat right out the window. This is one of the reason low-e windows helps. They actually reflect much of the heat back into the room so you literally feel less cold standing in front of a low-e window than a conventional one.
DIY Retrofits
Cellular shades
If you’re looking for a really effective cure to improve these cold-weather chills, look into cellular shades, like shown above. I installed these some years ago even though I already have high-tech, super insulating windows. Why? Because they work! Really well, in fact. For about $100-$150/window, you can get them and install them yourself in an afternoon if you’re a little handy (it just requires the ability to make some measurements and screw in a few screws).
Window quilts
This is exactly what it sounds like – quilts for your windows. They can work amazingly well and don’t have to break the bank. It can be as simple as a rectangular frame covered with quilt material, sized to fit snugly in your window opening. Or, as fancy and expensive as a motorized system with special tracks that provide push-button control or even automated opening and closing.
Here’s a Google search where you’ll find all sorts of information on these quilts for your windows.
And here’s a great, practical article from 1983 in Mother Earth News.
One word of warning:
They work so well that when you open the shades in the morning, you might find condensation or even ice on your windows. Please, grab a towel and wipe the water. You don’t want water sitting on your wooden window sills every morning or eventually it may lead to mold growth and/or wood-rot.
Ted's Energy Tips 
Great post Ted- I’m glad you covered something like this because despite its basic nature, you’re right that a lot of people neglect this. Drawing the curtains- will the effectiveness depend on the material or is it your opinion that any will simply keep in the heat?
I’m partial to heavy curtains. The main thing is that they should be resistant to air movement. I know some people use heavy, quilted curtains to good effect. But I’ve got some rooms with simple lined bamboo shades and these work quite well also, though definitely not as warm as heavy cloth ones.
Thanks Ted. I shared it on https://www.facebook.com/EnergyEfficiencyisCool
Thank you Jim!
I also got notification of your contribution to the cause. I really appreciate it! Keep up the great work.
But not if it’s sunny and south facing! 😉
Glad you brought this up Eric. I should have mentioned that this is mainly a nighttime tip but it also applies during the day to windows that don’t get sun. While we usually open those shades too just for ambiance, we’re doing so at the expense of some heat.
This brings up the passive solar house. It’s not commonly known (among the non-energy-geeks) that windows sold these days are no good for passive solar heat gain during the day because of low-e coatings. These coatings are designed to reflect heat. That works in both directions so you don’t get that great, warm feeling sitting in the sun behind a modern window. Remember when we were kids, hanging out in front of a thin, single glazed window on a sunny day? It was wonderfully warm. No more 😦
In fact, when replacing my windows, I tried pretty hard to get the manufacturer to sell me windows that weren’t low-e for the south face of my house so that I could maximize the solar gain and they wouldn’t do it. Since I was committed to that manufacturer, I was stuck with basically no solar heat gain. The upside is that I don’t lose as much heat at night. But it would be really nice if you still had the high solar gain option from all the manufacturers.
I recently put in a bunch of new south windows as part of a renovation, and waffled on what to spec for solar heat gain. In the end, despite being in Minnesota (where it’s currently -15F), I went with middle-of-the-road coatings. Problem is, we also have 100F+ days in the summer, and I couldn’t convince myself that the tradeoff would be worth it. We do still get heat through the windows, maybe just not as much as we might have.
I did some modeling in REM/Rate and didn’t actually see a huge benefit, once I took into account heating as well as cooling loads with the change. (We don’t usually run AC, though, so maybe it would have been ok? On the other hand, maybe we would have had to start using AC more if we had high SHGC windows on the south in the summer….)
Those calculations are pretty telling. It seems like for “real life” use in mixed climates, the low-e windows are a good choice. I know I’m not diligent enough about pulling the shades at night so, as you noted, the overall gain would probably be minimal if I had gotten plain glass.
The good thing is if one can make it “brainless” using overhangs and foliage to block the summer sun while letting in the winter warmth. But I’d probably still forget to close the curtains at night!