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U-Factor and Solar Heat Gain Coefficient Definitions

As a follow up to our previous post on State Required Energy Codes For Windows, here are some definitions for U-Factor and Solar Heat Gain Coefficient (SHGC).

The U-factor is a rating given to a window based on how much heat loss it allows. U-factors generally range from 0.2 (very little heat loss) to 1.2 (high heat loss). The U-factor is the inverse of the R-value of a window, which measures a window’s insulating value. Thus, a high R-value is the same as a low U-factor, and means that a window does not allow much heat to escape.

A poorly-made window cannot get a low U-factor. Single-pane windows are about 1.0 and double-pane windows are about 0.4. If you live in a colder climate, or find that you are always heating your home, buying windows with a low U-factor is a good way to save energy and money. The National Fenestration Rating Council (NFRC) offers reliable U-factor ratings for windows that they have certified.

The Solar Heat Gain Coefficient (SHGC) is a number assigned to a window that tells you how much heat that window lets pass into your home from the sun. SHGC numbers range from 0 to 1, and the lower the number, the less heat will enter your home. Thus, in hot climates a low SHGC is desirable, while in cold climates a higher SHGC is desirable. The National Fenestration Rating Council (NFRC) offers reliable SHGC ratings for windows that they have certified.

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State Contractor's License: 724532 B, C17