The NFRC label contains performance data:
U-factor and Solar Heat Gain Coefficient (SHGC) are particularly important from an energy consumption perspective, but the Visible Transmittance and Air Leakage ratings are very important from the standpoints of occupant comfort and visual appeal.
The NFRC rating and labeling program ensures that builders and consumers obtain reliable energy performance data. For further information visit the NFRC's discussion of its Energy performance label and its Certified Products Directory.
The ENERGY STAR® program identifies what are generally considered to be well-performing window products.
The ENERGY STAR® Windows program, created by the Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA) encourages consumer preference for energy efficient window products.
THE ENERGY STAR® label was created to help consumers identify energy efficient products. Look for this ENERGY STAR® label the next time you purchase windows. To achieve the ENERGY STAR® designation, a window must have U-facor and SHGC ratings below specified minimum values. Because energy efficient window performance varies by climate, these values vary according to three different cooling climate zones. In order to meet ENERGY STAR® requirements in Texas the Solar Heat Gain Coefficient (SHGC) must be less than 0.40 in the Panhandle, less than 0.30 in Central Texas, and less than 0.27 in South Texas. U-factors must be kept below 0.32 in the Panhandle, 0.35 in Central Texas, and 0.60 in South Texas.