Window Heat-Loss Rant

My Annual Window Heat-Loss Rant.

home heat-loss graphicIt would seem that winter is winning the battle against autumn. Again. Which means that our heating bills will start to go up in direct proportion to the temperature going down.  Because at least 25 percent of your home heating bill goes out the windows, I thought it was time for me to do my annual “ Do you realize how much money is going out your windows?” tirade.

Yup, twenty-five percent of your heating bill goes out your windows. “But,” you decry,” I have triple glazed, top-of-the-line, low-E brandy-spankin’ new windows. They don’t allow this much heat through.” Yes, they are better than single-pane windows, but surprisingly not by much.  Lets face it, when we are talking $25.00 of every $100.00 in heating costs just disappearing, we need some proven, quick and functional answers to the heat loss problems rather than 5 or 10 percent changes in insulating values.

u-value to r-value tableA super window will have an R-value of about 4. The wall beside it is R-24. A single layer of venetian blind or unlined curtain, will give you an additional R-value of 1. Add a lining to the drapes, or substitute a cellular shade and the R-value jumps to maybe 3. (If you use a triple cell shade, with an inner cell, you might get an R-value of 7 or 8. ) Add a drapery treatment with a blackout lining and interlining  to the cell shade and you are up to 13 or 14. Add a board-mounted valance above the drapes and you could get up to an R-value of 15 or 16. Not bad. And you will decrease your heat loss by about 50 percent.There will be some engineer types out there who say that the correct way to measure window heat loss is by U-value, not R-value and they are right. But most of us have a hard enough time with R-value, and the figures I use here are U-values converted to R-values through and I don’t make this stuff up. ( Click on the graphic for the source website.)

Energy films applied directly to your windows (such as EnergyFilm) can reduce heat loss by up to 35 percent. And the stick-to-the-frame clear plastic can increase the U-value of the window by up to 90%.

A few years ago my sister-in-law Judy Erlam and I developed a software program that will calculate the amount of money you are actually sending out your window, and how different window coverings will affect that loss. We started with this information from the University of Wisconsin. And, in full disclosure, Judy was the brains behind making this software actually work.  If you would like to find out how much money you are sending out your windows, email me.

So there you go. You are sending up to $25.00 of every 100.00 of your heating bill directly out your window. But you CAN reduce this loss.

Here’s  a cool graphic which clearly shows the heat loss on windows and what the simple addition of solar window film can do.:











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