U-Value and SHGC Window Ratings

In 1989 the National Fenestration Rating Council was developed to standardize ratings for windows. Energy-efficiency ratings for windows can be found by looking at the U-value and Solar Heat Gain Coefficient (SHGC). Ask your retailer or window manufacturer for these ratings before you purchase to make sure you are buying the most efficient window for each side of your home.

  • U-value rates the heat energy either gained or lost. The lower the U-value number, the more efficient the window will be in conserving energy.
  • Solar Heat Gain Coefficient rates the fraction of solar radiation that penetrates the window. The lower the SHGC number, the less solar heat the window allows.

Especially living in the mid-South and Southern US, you can apply the “.30/.30” rule as a good place to begin when doing your research. A U-value of 0.30 is considered good. Both U-value and SHGC under 0.30 is the best place to start. Consider the sides of your home and how much sun protection you want to achieve. You may want to install Low E3 Argon gas windows on the west and/or south sides of your home for extra protection against summer afternoon heat. You could install Low E Argon gas or Low E windows on other sides to save some money on product price.

Conserving energy helps us all. With the price jump in energy costs over the past few years, window replacement can be a noticeably significant value to your future energy savings as well as comfort in your home.