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Replacing your windows can be the most costly and least cost-effective energy efficiency investment you can make. But there are sound reasons, besides energy efficiency, to invest in new windows, such as comfort, resale value and aesthetics.

If reducing your energy costs is important, you should weigh an investment in new windows against the other energy efficiency opportunities you may have, such as adding insulation or purchasing a new heating and cooling system. An energy audit by your local electric cooperative or a qualified auditor is the best way to compare your options.

The auditor can perform a diagnostic test to determine how leaky your windows are. These tests often show that windows, even older ones, aren’t as leaky as you might think – and that you have more significant air leakage problems elsewhere in the home. You also may discover there are ways to reduce heat loss through your windows without replacing them, such as storm windows or window coverings.

As you begin to explore window replacement, ask yourself if you’re happy with the number of windows you have and with their sizes and locations. You could, for example, decide to increase or decrease the size of a window – or to replace a window with an exterior door. Sometimes these types of changes are quite affordable, but the cost can be much greater if significant changes to wall framing are required.

When considering whether to add more windows, remember that even very efficient ones are much less effective insulators than a home’s exterior walls, which means they’ll be colder to the touch than the wall in the winter. And, depending on orientation and shading, windows can let in too much direct sun in the summer, driving up indoor temperatures and air-conditioning costs.

When buying windows, you have a number of choices to make. Double-pane windows are necessary to meet code for most applications, but the additional cost for triple-pane windows could be worth the investment. Choosing argon or krypton gas between the panes adds a little more efficiency. 

A common option that’s well worth the investment is a low-emissivity coating added to the glass. The most important benefit of this  “low-e” coating is its ability to reflect heat back into the interior space, which reduces heating bills and increases comfort. These coatings reduce solar heat gain during warm-weather months as well, which can help lower air-conditioning costs. 

Also consider window-frame construction, with materials including wood, composites, fiberglass, aluminum or vinyl. Each has pluses and minuses in terms of cost, maintenance, durability and energy efficiency.

Fortunately, windows are rated for energy efficiency, so you don’t need to know all the details about their construction. The most important indicator of a window’s energy efficiency is the U-Factor, which measures the rate the entire window loses heat. The range goes from 0.20 to 1.20, and the lower the number, the better a product is at keeping heat in.

Another number you need to check is Solar Heat Gain Coefficient, which measures how well a product can resist unwanted heat gain, which is especially important during summer cooling season. The lower the number from 0 to 1, the less you’ll spend on cooling.

Also look for an Energy Star® label. Only windows that are substantially more efficient than the code requires receive the Energy Star label. Check the website at for a list of windows, doors and skylights that qualify for the Energy Star label. Another good source of information is the National Fenestration Rating Council, a nonprofit organization that establishes objective window, door and skylight energy performance ratings to help you compare products and make informed purchase decisions; visit

Bids for new windows vary a great deal, so it’s worth requesting more than one and comparing qualifications of the contractor, as well as price, for something that will change the look and comfort of your home for many years to come. Air leaks and moisture problems are common if windows aren’t installed properly, which can create mold, mildew and rot in the wall. Moisture also can prevent a window from operating properly or cause trim paint to peel.  

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