Windows, Part II: The NFRC Label

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In Part I of my series on windows, I talked about low-E coatings which enhance a window’s efficiency. Today, I’ll discuss the NFRC (National Fenestration Rating Council) label which appears on all products certified by the third-party, non-profit, and on all window, door, and skylight products rated by ENERGY STAR®. The NFRC label provides detailed information regarding a window’s performance and gives ratings for U-factor, Solar Heat Gain Coefficient (SHGC), Visible Light Transmittance (VT), Air Leakage (AL), and Condensation Resistance (CR).

The U-factor, or U-value, indicates the rate at which heat is lost through the window assembly. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value. The Efficient Windows Collaborative explains what type of U-factor is appropriate for the four climate regions of the United States.

The Solar Heat Gain Coefficient (SHGC), expressed as a number between 0 and 1, tells you how well the product blocks heat caused by sunlight. If you live in a cold climate, you’ll want to allow more solar heat gain to help heat your living spaces, therefore a high SHGC is recommended. If you live in a warm climate, a low SHGC is better to help minimize air conditioning costs.

To maximize the amount of daylight that enters a space, you’ll want to choose a window with a high Visible Light Transmittance (VT), which typically varies between 0.3 and 0.8.

If you don’t want drafty windows, be sure to select windows with a low Air Leakage (AL) value of 0.30 or lower. This means less air will pass through cracks in the window assembly.

If condensation on the inside of your current windows is a problem, then be sure to check out the Condensation Resistance (CR) rating (between 0 and 100).  This measures how well the window resists water build-up. The higher the condensation resistance factor, the less build-up the window allows.

This ‘window selection’ tool is helpful to compare energy usage costs with different window options.

Tag(s): Energy, Greenhouse Gas Emissions / Global Warming, Greening the Home, Greening the Office

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