A Trick to Reduce Heat Loss Through Windows

I’m going to be traveling off to teach a couple workshops soon. When I’m away from home I also drop out of the cyber world, so don’t expect much to be happening in the blog for a little bit. Still, before I leave I wanted to cover one other winter themed item. My wildly optimistic hope is that by the time I’ve returned March will have made its shift to spring like weather! Yeah, I know, we’ll probably all be laughing about this under several feet of snow at the end of the month, but a guy can dream.

(Please note some of the links in this blog post are affiliate links. What this means is that should you click through them and make a qualifying purchase I will receive a commission which I’d certainly appreciate since it helps support this blog project. However, this shouldn’t increase your cost any, and certainly don’t ever feel like I’m pressuring you to buy things through the links I offer or anywhere else. I’m all about being frugal first!)

What I wanted to write about today is again a relatively simple, practical thing, window coverings. It used to be that when the serious cold snaps would happen, plunging temperatures into the negative degrees, I would just feel the chill dropping down off the window over my bed at night, freezing my face. Then one night, annoyed and cold, I shoved a bunch of clothes up along the window ledge. That seemed to help a lot!

About that same time I was reading a book by John Michael Greer called “Green Wizardry”. The longer title is “Green Wizardry: Conservation, Solar Power, Organic Gardening, and other Hands-On Skills from the Appropriate Tech Toolkit”. This longer title pretty much sums up what the book is about. I expect you’ll find me referring to Mr. Greer fairly often in future blog posts since, to me at least, he is one of the leading thinkers of our time, perhaps because he seems to have such a command on our past history. Anyway while most of his books are focused more on concepts that shape our culture this book is more about physical projects one can do. Among the many wonderful, practical things in the book was a section on something once common enough, but since discarded by our culture to the point where I had never heard of it. This is the idea of window coverings. Duh! Why didn’t such a thing dawn on me before. I know windows have horrendous R-value so naturally making a covering to put up at night when there is no potential solar gain would be a good idea.

The basic idea is this, you make an insulated plug to fit each window. When it’s cloudy, at night, or in rooms not being used, you insert them. During the day when you want to let some light in, and hopefully some solar radiation to help heat the home, you remove them from the windows.

There are many ways one could make them, and they could certainly be made better than what I’ve done. Out in my studio I have rigid foam inserts covered with fabric. Those are nice and have a much higher R-value than what I made for my home. The downside to them is that they take up a lot of space when they aren’t in the windows.

What I made for my home was going to be fancier, but in the end I went with quick and functional. I was able to score some really cheap double bubble reflective foil insulation from a friend who got rolls of it for next to nothing at an auction. I see the price of it on Amazon isn’t too bad if I had needed to buy it new. Basically it’s metalized bubble wrap. The foil part can reflect radiant heat back into the room, while the bubble part is simply trapped air space to insulate. I cut this bubble insulation so it was a little bit bigger than the window frame. I want it to bend in and snug up all around, rather than being short and leaving gaps.

With this as my base I then went to the fabric store and got a bunch of polar fleece in both black and white. The black I used for the side facing the window since black will absorb more of the sun’s heat rays should the inserts be in place when the sun is up. The white I used to face indoors to help brighten up the room a bit. Like with the bubble stuff I cut this to be a bit large so there wouldn’t be gaps.

Next I cut some thin strips of scrap wood to use as spacers between the layers, creating yet another dead air space as well as providing a bit of rigidity to the whole thing. I carefully measured and cut these wood strips to length so they would fit snugly in each window frame.

Originally I thought I was going to drill some aesthetically arranged holes in the wood strips and neatly sew all the layers together. I’m sure that would have looked nice and worked well. However, once I set about actually doing that I realized that despite the fact I can spend weeks chasing fine details into metal vessels I just didn’t have the patience to do that sort of sewing. Staple gun to the rescue! With that tool these were made in a hurry!

I should probably note the reason you want a snug fit into the window frame rather than just drapes in front of the windows. If you have an air gap at the top and bottom what can get set up is a convective anti-chimney effect. The air trapped in the space between the curtains and cold window gets colder. Colder air will fall down under the curtains and into the room. At the same time as the cold air is falling it is drawing warm air in the top to fill the space. This new air gets chilled and drops away continuing the cycle. So if I was just using curtains, or my window inserts have gaps at the top and bottom then I could be generating a flue effect and actively working to cool my room instead of retaining the heat!

John Michael Greer also recommends that there be a vapor barrier on the side of the insulation nearest the interior space to help prevent condensation on the window. With my inserts the plastic bubble stuff performs this function.

I had initially thought I’d rig up some way to roll these to the top of the windows each day. Once I had the basic thing made I realized it was much easier to just roll them down rather than up. This way I didn’t need any sort of strap to hold them in place. Gravity does the work for me. I found there is another benefit to this bottom storage method. It creates a little cold well in the trapped space between the window and rolled up insert. The cold air from the window drops down into it, but since it isn’t open at the bottom it can’t keep falling into the room. I think of it as being rather like those open topped freezers you see in some supermarkets. You would think they would be wildly inefficient essentially being a freezer with the door open all the time. Yet, because cold air wants to fall they actually work out alright. (I still have to wonder if they are less efficient.)

So the question is, just how well do these work? Are they really worth the effort to make and take in and out of the windows each day? I felt like they were worthwhile having used them for a few years, but I never really had any numbers to back it up. Then in order to gauge the performance of my rocket mass heater I bought a nifty little toy, an infrared temperature gun. I’ve found it well worth the money for understanding how my heater is working, but it’s also been useful in letting me easily gauge temperature performance in other things, such as my window coverings.

Those of you living in the Midwestern part of the US may remember that nice polar vortex we had earlier this winter that set some invigorating new record lows. I chose to use one of those nights to run my test. My rocket mass heater finished its burn in the evening and was out all night. It was so cold that night the storage mass of the heater wasn’t enough to keep it above 58 degrees F inside. Sometime in the wee hours of the morning the propane furnace began running a bit to keep it at 58. First thing in the morning I went out and using my temp gun took a reading on the outside of the house near the window. It was -13.5 degrees F! Then I measured the side of the window insert facing into the home. It was 56.3 degrees F. Finally I rolled down the window covering and took a reading on some frost on the inside of the window. I couldn’t take a measurement on the window itself since that won’t reflect back the infrared well enough. This measured 6.5 degrees F.

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So, crudely speaking, the window itself provided a difference from -13.5 to 6.5, or 20 degrees F. The window insert gave a difference from 6.5 to 56.3, or 49.8 degrees F. This means the window insert, a slapped together construction of fabric and bubble wrap, increased thermal performance about 250%! I’m happy with that!

When the weather warms up I bundle all my window covering together, stuff them into a big bag, and store them away in an outbuilding until winter rolls around again. The thing I really need to do before storing them this year is mark which one goes to which window. Otherwise it’s something of a game test fitting similar sized ones to each window, because they are all individually fit to be snug on each specific window. I must admit I’m also thinking I might make some better ones from rigid foam for the interior windows where I tend to just leave them up all the time. These are windows where it’s just a pain to get access to, as well as the back room which I basically use just for photography (and want the windows blacked out anyway).

So if you are looking for another way to cut your heating bills and stay a bit more warm and snug in the winter I might suggest making up a set of window inserts for your home. They could certainly be fancier than mine, but they don’t need to be.

Studio Snippet

Since I both mentioned how I essentially only use my back room as a photo studio when I finish a batch of work, and I happened to finish a batch of work yesterday I thought a couple shots of this set-up might be in order for today’s studio snippet.

It’s a fairly basic, cheap, if not crude rig, but it’s been getting the job done for me for many years now. The base of it is a 4′ x 8′ sheet of white tile board that I clamp down to a folding table and arch back up onto the wall. Then I got a couple of those plastic diffusion screens commonly used in the standard 4 tube florescent light fixtures. I got these really cheap, if not free, because the corners were already broken making them really really hard for the store to sell. The slightly broken corner didn’t matter at all for my use. So I arched these over, holding them in place with a few volumes of the World Book Encyclopedia. (Hey if nothing else a 1979 edition of the encyclopedia make good weights!) Next I cut a sheet of foam core to fit the arch of the diffusion and add additional sheets to block excess light from shining on the back section of the tile board. This created the graduated backdrop.

Then I set up the three lights, a key, fill, and back light. A couple more scraps of foam core help shade and direct the light. My vessels to be photographed are lined up on the counter and I just go down the line taking the photos. I used to use real 500 watt photo flood lights. I’ve since switched to the normal LED lights I use all the time around the homestead. Today’s digital cameras seem to compensate fairly well, though I do admit to doing a fair amount of post production work in photo editing programs.

I’m happy to have a site where I can again allow comments. (I had to shut them off on my main website because the spam was simply uncontrollable!) So please I encourage you to share thoughts of your own. My general rule about comments though is just to play nice. Differing views are fine, but I’m not interested in engaging in or moderating verbal fights. If I feel things get out of hand, by whatever criteria I decide, I’ll just start blocking or deleting things.