Independently Tested and
Certified Energy Performance

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 National Fenestration Rating Council (NFRC).

NFRC is a third party, non-profit organization that sponsors certified rating and labeling programs to help consumers compare the energy and performance features of windows, doors, and skylights.

NFRC's programs do not distinguish between "good" and "bad" windows, set minimum performance standards, or mandate performance levels. This is where ENERGY STAR comes in. ENERGY STAR enables consumers to easily identify NFRC-certified products with superior energy performance.

Performance Ratings

• U-Factor measures the rate of heat transfer and tells you how well the window insulates. The lower the U-Factor, the better the window insulates. U-Factor values generally range from 0.25 to 1.25. Find the ENERGY STAR U-Factor for your region.
  
  

• Solar Heat Gain Coefficient (SHGC) measures the fraction of solar energy admitted and tells you how well the product blocks heat caused by sunlight. The lower the SHGC, the less solar heat the window transmits. SHGC is measured on a scale of 0 to 1; values typically range from 0.25 to 0.80. Find the ENERGY STAR SHGC for your region.
  
  

• Visible Transmittance (VT) measures the amount of light the window lets through. The higher the VT, the more light you see. VT is measured on a scale of 0 to 1; values generally range from 0.20 to 0.80.
  
  

• Air Leakage (AL) measures the rate at which air passes through cracks in the window. AL is measured in 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 cfm/ft².
  
  

• Condensation Resistance measures how well the window resists water build-up. The higher the condensation resistance factor, the less build-up the window allows. Condensation Resistance is scored on a scale from 0 to 100. The Condensation Resistance rating is useful when comparing different products.
  
  ENERGY STAR qualification is based on U-Factor and SHGC ratings only.