ENERGY STAR qualified windows meet a stringent energy efficiency specification set by the Department of Energy and have been tested and certified by the NFRC (National Fenestration Rating Council). The NFRC is an independent, third-party agency that maintains a database of certified window and door energy performance information. The information includes U-factor, SHGC (Solar Heat Gain Coefficient), VT (Visible light Transmission) and other data.
ENERGY STAR qualifications are based on U-factor and SHGC ratings for each of four different climate zones (see map below). To be ENERGY STAR qualified, a window or door must meet the efficiency standard for the climate zone where it will be used.