Performance Reviews

Anderson

When it comes to picking replacement windows, it might seem like a no-brainer to look for models that have the best energy-performance ratings. After all, for at least the rest of 2010, you qualify for as much as $1,500 in federal tax credits if you buy windows that do the best job of keeping heat from the sun out of your house and heat from your furnace in.

But even if cost were no problem, buying windows that have the best performance ratings often isn’t the best thing for your home or for your wallet. Making a decision that is based on the performance guidelines that are tied to the current tax credits unfortunately means that consumers rely on what amounts to a one-size-fits-all performance threshold that often steers consumers to make the wrong choices.

We interviewed independent energy-efficiency experts and examined annual energy costs that are related to the expected performance of the latest replacement windows. We concluded that depending on where you live you could pay a premium for performance levels that you’ll never need. What’s worse is that you could buy a replacement window that does as much harm as good, because it keeps out the sun’s heat when you want it most.

Even if the federal tax credits disappear after 2010—and at press time, it was uncertain what will happen—the consequences of performance ratings that are tied to those incentives could linger for years to come and distract consumers from making choices that are best for them.

RATINGS TRUTH. When it comes to performance ratings in 2010, the critical numbers to remember—and the combination to largely avoid—are 0.30 and 0.30. Windows that have a U-factor rating of 0.30 or less and a solar heat-gain coefficient (SHGC) of 0.30 or less qualify for the aforementioned credit. Consequently, these numbers have created a misleading target. U-factor measures how well a window keeps heat in your home; SHGC measures how well it keeps out the sun’s heat.

Experts say these two variables are the most important factors in measuring the energy efficiency of a window and that a rating of 0.30 or lower in each category is considered to be excellent. However, because different regions have different climates, homeowners generally will benefit from purchasing windows that have ratings that are excellent in one—but not both—of those categories. In other words, someone who is in sunny Florida would want a window that has an excellent SHGC rating (to keep the sun’s heat out) but wouldn’t need a window that has an excellent U-factor rating (to keep the heat from your home-heating system inside).

Conversely, someone who lives in Minnesota would want a window that has an excellent U-factor rating but not an equally great SHGC rating. A low SHGC rating (lower meaning better performance) means that a Minnesotan would waste the sun’s free energy, which can lower energy bills by reducing the amount of heat that a furnace must produce.

The notion that U-factor and SHGC ratings that are best for your home can vary by region is worth emphasizing now more than ever, because the one-size-fits-all performance guidelines that are attached to the tax credits have driven consumers away from considering climate. After the American Recovery and Reinvestment Tax Act established new performance guidelines for tax-credit-eligible products in 2009, manufacturers made significant adjustments to their window lines (such as improved glazing) to produce more windows that are eligible for the tax credits.

Yet it is possible that the windows that qualify for tax credits will drive up your heating costs so much that the $1,500 that you gain in tax credits will be erased by extra heating costs over the long haul. In one scenario of our analysis, a window that qualified for the credit added $1,500 to the total cost of heating bills in a home in less than 6 years. (See “Blanket Equation.”)