When you’re choosing new or replacement windows, it’s always good to look for the Energy Star label. But the information on each window’s NFRC label allows you to delve deeper and find the best match for your particular needs.

Hundreds of window, door and component manufacturers belong to the National Fenestration Ratings Council and submit their products to be rated for energy efficiency. The NFRC’s distinctive label on each of its members’ windows rates several categories – different features may be more important in your particular situation, but in general all the ratings measure how well the window keeps the inside in and the outside out.

The U-Rating measures how well the window keeps heat from escaping – an especially big issue in the winter when you want to keep that expensive heat indoors. The lower the number (on a range between 0.20 and 1.20), the less heat escapes.

The Solar Heat Gain Coefficient measures how much heat the window lets in with the light – particularly of interest in those southwest-facing windows, perhaps. When you want to keep the A/C bills low, look for windows with a low solar heat gain coefficient.

Visible Transmittance measures (on a scale of 0-1) how much light the window allows to pass through; the higher the number, the more light is transmitted.

Air Leakage looks at one of the biggest culprits in a home’s unwanted gains and losses of heat: flow of air through less-than-perfect seals and other joints on the windows. The lower a window’s AL number, the less air it lets through.

Consult with your window contractors about which features are most important to your project and learn more about energy star windows.

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