Energy Ratings for Windows

There are many energy ratings for windows (and other products). They can be broken down into different categories;

Solar Heat Gain Coefficient (SHGC) is a measure of the amount of outdoor heat that can enter the room.

R-Value is a measure of thermal resistance. It gives an indication of how quickly windows (or other materials) will lose heat.

U-Value is used to measure heat gain or loss through glass between indoor and outdoor air temperatures.

Visible Transmittance is measured from how much natural light can come into the room.

Air Leakage (AL) measures how much air will enter the room through the window (or other product).

The numbers are the most important aspect of the information;

  • The lower number for Solar Heat Gain Coefficient the lower potential for wasted cooling expenses.
  • The higher number the R-Value is the better the glass.
  • The lower number the U-Value is the lower the potential for wasted heating expenses.
  • A higher number for Visible Transmittance means the more light will come into the home.
  • The lower number for Air Leakage the lower potential for a draft.

These ratings are provided by the non-profit National Fenestration Rating Council (NFRC) who test, certify, and label energy efficient windows, doors, and skylights.

NFRC Label

Have more questions? Contact us today for more information 519-268-6331.