money out the window

3 Ways to Reduce Heat Loss through Windows.


It’s that time of year. Again. You get to listen to my “20 to 30 percent of your heating bill is going out your windows” rant.  I had to turn on the heat the other week. But I’m going to hold out for at least two more weeks before I get out the sleep socks and the  keep-warm-in-the-middle-of-the-day-sweaters. I hate this.

But I digress. If you feel a breeze around the edges of your windows or doors, if you get frost buildup on any part of your windows, and most importantly, if you can put your hand on the glass and it feels cold, you are in need of either a window tune-up, new windows or some upgraded window coverings.

First of all, we measure the insulation factor of a solid wall as the R-value, which is Resistance to heat loss. Windows are actually measured with a U-rating.

“U-Factor measures the rate of heat transfer and tells you how well the window insulates. U-factor values generally range from 0.25 to 1.25 and are measured in Btu/h. ft² °F. The lower the U-factor, the better the window insulates” ( 1)

But who knows about the U-factor of a window? Nobody, so that is why windows are most often listed as having an R-value.

Tune-up your windows.

You can look into replacing the weather stripping on the windows. There are a lot of different types out there;  the U.S. Department of Energy has a good description of the different types, application, and their advantages/disadvantages. They say that good weather stripping can reduce heating costs by 20%. (2)

They work to reduce the leaks around the edges; they do not increase the actual insulating value of the window itself. For example, a single layer of glass in an old window will not suddenly become energy efficient if you add new weather-stripping.

New windows.

The best solution, of course, is new windows. Your windows may just be old and worn out. Yes, that happens. The average lifespan of windows depends on a lot of things, and McGarry and Madsen spell it out quite nicely. (3)  Their link to how the lifespan is calculated lists their very respectable sources. Long and short of it: If you are dealing with windows more than 20 years old, and particularly ones with a metal frame, they are basically done.


Upgrade the window coverings.

This doesn’t have to be drastic as it sounds; if you use what you have and add layers – or get a good first layer started, you can see a substantial heat-loss reduction right now.

I have a layered window covering on my balcony sliding door. I have five layers now. There is a rod with a semi-sheer next to the window which provides privacy in the summer. I can leave the doors open for the breeze, and the curtains look after the lookie-loos. On another rod I have a medium-weight drapery which is lined with a flannel-backed lining. That’s my summer and spring window covering. It’s not blackout because I like having the ambient light. Between that treatment and the semi-sheer, I have added two layers of insulating material which hangs on the curtain pins for the drapery. 

So, quick calculation. If I can save 20% on my heating bill, I can pay for the window treatment in 2 years. 

Here’s why: Balcony doors: maybe an R-value 4 if I’m being really generous. ( Remember that the walls are R-24; R-0 is a hole.) The sheer maybe adds a 1, the drapery fabric 1, the flannel lining 2, the two extra liners two each.. so now I’m up to R-12. Which is a whole lot better than verticals, or a one-layer pre-made panel, or a Venetian blind.  If I added an insulated Roman shade which attaches to the wall at the sides, and a valance to prevent heat loss up the top of the drapery, I could conceivably get up to an R-value of R-18 or more. Which is pretty darned good.  The BEST windows on the market offer an R-value of 8. I heard there was one coming which is greater, but it’s not commercially viable yet. (4)

So why bother with all this? To reduce the amount of money I have to give to BC Hydro for my heat. That simple.


1.   U-factor:

2. U.S. Department of energy: types of window sealing products.

3. McGarry and Madsen

4. I based my calculations on data available from several blind manufacturers and window treatment manufacturers. For more info

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