What the National Fenestration Rating Council (NFRC) has to say
The NFRC is the leader in energy performance rating and certification programs for fenestration (windows and doors) products.
Compare Product Performance
The NFRC label provides information on how a window performs. The two most important energy ratings are U-factor and Solar Heat Gain. By reviewing the label information, consumers can make an informed choice about the product that is best for their individual situation.
What is U-factor?
U-factor is also known as thermal transmission. It is a measure of the rate of heat loss through a product. Therefore, the lower the U factor, the lower the amount of heat loss. In cold climates, where heating bills are a major concern, choosing windows with lower U-factors will reduce the amount of heat that escapes through a window from inside your house to the outside.
What is Solar Heat Gain?
The Solar Heat Gain Coefficient, also known as SHGC, measures the rate of heat gain through a product. Therefore, the lower the SHGC, the lower the amount of solar heat gain. In hot climates, where air-conditioning bills are a major concern, choosing windows with lower SHGC will reduce the amount of heat that comes in through your windows from the outside.