An opening in a building's envelope is called Fenestration, a term that includes windows, skylights and doors. Since 1993, new windows began carrying energy efficiency labels from an organization called NFRC -- the National Fenestration Rating Council.
NFRC is a non-profit, public and private organization created by the window, door and skylight industry. Its membership includes manufacturers, suppliers, builders, architects and designers, building code officials, utilities and government agencies.
NFRC's primary goal is to provide accurate, standardized information to consumers, making it possible to measure and compare the energy performance of window, door or skylight products.
The NFRC label describes the type of window, and rates it for these factors:
U-factor is a measure of how well heat is transferred by the entire window -- the frame, sash and glass -- either into or out of the building. The lower the U-factor number, the better the window will keep heat inside a home on a cold day.
Solar heat gain coefficient (SHGC) is a measure of a window's ability to transmit warmth caused by sunlight. A lower number means less heat is getting through, resulting in reduced air conditioning costs during the hot season.
Visible light transmittance measures how much light gets through the window. A window with a high number will allow more natural daylight into your home.
An NFRC label merely presents objective information. It does not distinguish between a "good" window and a "bad" window, nor does it set minimum performance standards or mandate performance levels.
When a manufacturing company decides to certify and label its products, it commits itself to provide accurate, fair and reliable energy-related performance information. This helps consumers, builders, and the fenestration industry itself.