Benefits of energy-efficient windows

Research into energy-efficient windows for a home renovation discovers some surprising benefits.


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    The last of the old windows still in place at Sheep Dog Hollow, a hundred-year-old house being renovated in an environmentally friendly way in East Haddam, Conn.
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I knew we wanted to put in high quality, energy-efficient windows for our renovation of Sheepdog Hollow simply because that appeared to be the right thing to do – especially since we opted to install geothermal heating.

For geothermal heating to work as efficiently as possible, your house has to be buttoned up tight, as insulated as possible. And so, obviously, we need to have energy-efficient windows that work to keep heat in and cold temperatures out.

As I began to do some research, what really impressed me about some energy-efficient windows has nothing to do with sustainability or heat loss. It has to do with cleaning.

Recommended: Think you know the odd effects of global climate change? Take our quiz.

Yes, some high-tech windows designed to screen out harmful UV rays and thus help make your overall heating and cooling more efficient also have an exterior coating that “reduces water spots up to 99%” and minimizes dirt buildup on the exterior.

So you can invest in highly efficient windows and say good-bye to at least some of those spring cleaning days dedicated to washing the outside of your windows.

That in itself was enough to convince me that the extra cost of installing energy-efficient windows (which can be as much as 15 percent more) was worth every penny.

I recognize that is not necessarily rational, but I hate cleaning the outside of windows, especially on the second floor.

That said, I recognize that rationality is important in ventures such as our renovation, and the tax credit of up to $1,500 for installing energy-efficient windows did help some with rationalizing his decision from a purely economic standpoint.

But forget economics for a minute. These windows are wonders, from my humble perspective. They have what are called Low-E coatings, which, stated simply, means they have invisible layers of metal oxides on them that reduce the influx of harmful rays.

The Efficient Windows Collaboration offers a more technical explanation:

Window Technologies: Low-E Coatings
Low-emittance (Low-E) coating are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. The principal mechanism of heat transfer in multilayer glazing is thermal radiation from a warm pane of glass to a cooler pane. Coating a glass surface with a low-emittance material and facing that coating into the gap between the glass layers blocks a significant amount of this radiant heat transfer, thus lowering the total heat flow through the window. Low-E coatings are transparent to visible light. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.

I had hoped that the Efficient Windows Collaboration would be a good source to find answers to some of my more pedestrian questions. Unfortunately, I found the site to be way too technical for me.

It’s probably best for professionals who don’t have to look up “U-Factor” when trying to understand how an energy efficient-window works. (Which, by the way, according to the website Ecomii is:

…. a rating given to a window based on how much heat loss it allows. U-factors generally range from 0.2 (very little heat loss) to 1.2 (high heat loss). The U-factor is the inverse of the R-value of a window, which measures a window’s insulating value. Thus, a high R-value is the same as a low U-factor, and means that a window does not allow much heat to escape.

So I turned to a much simpler to understand source: Bob Siekierski, the windows expert at Shagbark True Value, our local hardware store. (In our effort to renovate Sheepdog in as “sustainable” manner as possible, we’re also trying to use as many local suppliers as possible.)

When I first asked Bob about windows, he said: “They’re just glass and sticks.” Call that Connecticut dry humor.

In the next post: Bob’s explanation of how energy-efficient windows work – and why you don’t have to clean them. (And coming soon: whether we're using a closed-loop or an open-loop geothermal system, as well as what each of them means.)

Editor's note: Alexandra Marks will be blogging twice a week about her green and budget-friendly restoration of a 1902 farmhouse in Connecticut. See a photo gallery of the early days of the project by clicking here. You can read all she's written about the project so far by clicking here and then looking for Sheep Dog Hollow under Topics on the right side of the page.

You'll find numerous articles about the environment at the Monitor’s main environment page. Also, check out our Bright Green blog archive and our RSS feed.

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