Understanding Glass Performance

NFRC label sampleThe National Fenestration Rating Council (NFRC), a nonprofit organization, has defined labeling requirements for windows and doors. This information is provided to help you choose the best product for your home. Under the program, products are independently tested, certified and labeled, so you can be confident they will perform the way they are advertised. And as you will see, the ENERGY STAR program uses U-Factor, Solar Heat Gain Coefficient and Air Leakage to qualify products for certification.


Measures how well the window prevents heat from entering or escaping the home. Ratings generally fall between 0.2 and 1.25. Windows with a lower U-Factor provide better insulation. U-Factor is important wherever you live, but is a primary concern for homes in colder Northern climates.


Solar Heat Gain Coefficient (SHGC)

Measures how much heat from the sun is blocked. This number can range from 0 to 1 where windows with lower numbers reflect more heat. This is particularly important during the summer in hot Southern climates.


Visible Transmittance (VT)

Measures how much light comes through the whole window. Ranging from 0 to 1, windows with higher numbers allow more light into the home.


Air Leakage

Measures how much outside air comes into the home through a closed window. Rates typically fall in a range between 0.1 and 0.3*. The lower the air leakage number, the lower the potential for draft through the window.


Condensation Resistance (CR)

Measures how well the window resists the formation of condensation on the inside of the window. CR is expressed as a number between 1 and 100. The higher the number, the better the window is able to resist condensation.





*As of January 1, 2015, the lowest allowable rating for Air Leakage on the NFRC label for windows and sliding doors is ≤0.3. Sunrise Windows are designed and manufactured to deliver superior air leakage performance. Actual ratings as tested are provided by window type on the following pages.