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Select New Efficient Replacement Windows

3. Compare window energy ratings

There are energy performance differences among windows that meet the ENERGY STAR and federal tax credit criteria. Although virtually all qualifying windows have low-E coatings and most have gas fills, the type of low-E coating or gas may vary, there are many frame design options, and some products stand out with high-end features such as triple glazing. You can learn about different window technologies, but how they affect a window's energy performance depends on the sum of all parts. This is where whole window energy ratings help, accounting for the combined effect of glazing, spacers and frame.

The National Fenestration Rating Council (NFRC) label provides the only reliable way to determine whole-window energy properties and to compare products. The NFRC label appears on all window, door, and skylight products which are part of the ENERGY STAR program or qualify for the federal tax credit. NFRC ratings include U-factor, Solar Heat Gain Coefficient (SHGC), Visible Light Transmittance (VT) and optionally, Air Leakage (AL) and Condensation Resistance (CR).

NFRC sample label
U-factor U-factor
SHGC Solar Heat Gain Coefficient
VT Visible Transmittance
AL Air Leakage
CR Condensation Resistance

U-factor and SHGC determine whether a window qualifies for ENERGY STAR and the federal tax credit. A lower U-factor means less heat loss and is the priority in a cold climate; a lower SHGC means less solar heat gain and is the priority in a hot climate. ENERGY STAR criteria take these priorities into account. See ENERGY STAR recommended window properties.

The effect of the window properties on heating and cooling costs depends on the climate and the characteristics of your house.

4. Compare typical energy costs in your climate»

5. Select the most efficient windows for your specific house»