Funded by Southern California Edison Company’s Local Government Strategic Plan Strategies Program

under the auspices of the California Public Utilities Commission.

Window Energy Performance Ratings

The energy performance ratings on windows have three main factors that describe the efficiency of a window.

 

 

Solar Heat Gain

The percentage of the sun’s energy that passes through the glass to heat up the interior surface.

 

U-factor

Measures how easily heat passes through the entire window assembly—not just the glass.

 

Visible transmittance

Measures how much air can leak through the window.