The energy performance of all ENERGY STAR qualified windows, doors and skylights must be independently tested and certified according to test procedures established by the Performance Rating Factors
The NFRC label can be found on all ENERGY STAR qualified windows, doors and skylights and provides performance ratings in five categories:
U-Factor measures the rate of heat transfer and tells you how well the window insulates. U-factor values generally range from 0.25 to 1.25 and are measured in Btu/h·ft²·°F. The lower the U-factor, the better the window insulates.
Solar Heat Gain Coefficient (SHGC) measures the fraction of solar energy transmitted and indicates how the product blocks heat caused by sunlight. SHGC is measured on a scale of 0 to 1, with values typically ranging from 0.25 to 0.80. The lower the SHGC, the less solar heat the window transmits.
Visible Transmittance (VT) measures the amount of light the window lets through. VT is measured on a scale of 0 to 1, with values generally ranging from 0.20 to 0.80. The higher the VT, the more light you see.
Air Leakage (AL) measures the rate at which air passes through joints in the window. AL indicates the cubic feet of air passing through one square foot of window area per minute. The lower the AL value, the less air leakage. Most industry standards and building codes require an AL of 0.3 cf·m/ft².
Condensation Resistance measures how well the window resists water build-up. Condensation Resistance is scored on a scale from 0 to 100. The higher the condensation resistance factor, the less build-up the window allows.
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