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A Transparent Look at Energy-Efficient Windows: Cost, Effectiveness, and More

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Energy-efficient windows have been touted as a way to reduce your home’s energy loss. After all, your average pane of glass doesn’t do much to keep heat or cold inside your home, depending on what’s desired for the season. So energy-efficient windows are well worth considering for homeowners who want to control their costs.

(Thomas Trutschel/Photothek via Getty Images)

By Terri Williams

“Homeowners should know that including energy-efficient windows will not only keep your home comfortable and your residential heating and cooling costs down, but they will also raise the resale value of your home,” says Brian Gow, president of Scheel Window & Door.

In fact, 25% to 30% of cool air and heat escape through windows, according to, which can force your system to work harder and your bill to shoot up.

But is it actually worth investing in energy-efficient windows? Here’s what you need to know.

What are energy-efficient windows?

So, what differentiates an energy-efficient window from a regular window? A low emissivity (or “low E”) window coating made from nearly invisible metallic oxides on the glass pane suppresses the radiant heat flow throughout the window, according to Robert Himmaugh, manager at Acadian Windows and Siding. Such windows can range from $100 to over $1,000 depending on the size, he says.

But buying energy-efficient windows is not as simple as going to the store and asking for them; you need to know which type of windows would be best for your situation.

“Choosing the right energy-efficient windows depends on the region you live in, the severity of your weather, and if your house is exposed to extreme weather events,” says Anne Fairfax, co-founder of architectural firm Fairfax, Sammons & Partners, which has offices in New York City and Palm Beach, FL.

“We favor custom wood windows, with true divided light panes, double-glazed, for our high-end projects,” Fairfax says. “For our more budget-minded projects, we like to use Brosco windows, which is a traditional, well-priced wood window, which has optional interior storm panels.”

Understanding efficiency ratings

Double-glazed. U factor. What do all of these terms mean, and how do they affect the efficiency of your windows? Here are the key indicators of energy performance for windows:

  • U-factor: The lower the number, the more energy-efficient the window is. Michael DiMartino, senior vice president of installations at Power Home Remodeling, says you always want to look for a U-factor of 0.30 or lower.

  • Solar heat gain coefficient (SHGC): This measures how well a window blocks heat from sunlight. Again, a lower rating is the sign of a more efficient window.

  • Air leakage: This rating measures how much air passes through the joints of a window. A lower rating means less leakage occurs.

  • Visible transmittance: Sometimes, a higher number is important. Visible transmittance measures how much light a window lets through, and it’s ideal to get as much as you can.

  • Condensation resistance: This measures how well the window resists water buildup. Mark Montgomery, vice president of marketing at Ply Gem Windows, says homeowners should look for a higher rating in this case, as that marks a window that allows for less buildup.

  • R-value: This indicates the material’s resistance to heat flow, so the higher the better. Fairfax explains that a window with single glazing will have a lower R-value than a triple-glazed window.

  • Energy rating: This is a measure of the balance between the U-factor, SHGC, and air leakage.

Alternatives to replacing your windows

Energy-efficient windows can help you save money, but completely replacing your windows might not be in the cards right now.

Applying a low-E coating on your existing windows (on the interior or the exterior) can improve their energy efficiency, according to Himmaugh.

There are other ways to improve energy efficiency. For example, Fairfax says, your window treatments can make a difference.

“Insulated curtains can help increase energy efficiency by keeping out the cold,” she says. “For dealing with heat gain, inexpensive natural blinds can be installed on the exterior of the windows.”


Terri Williams is a journalist who has written for USA Today, Yahoo, the Economist, U.S. News and World Report, and the Houston Chronicle.

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