SHGC

What Is Solar Heat Gain Coefficient?

Solar Heat Gain Coefficient (SHGC) measures how much solar heat passes through a window into your home. It is expressed as a number between 0 and 1. Lower values mean less solar heat enters, reducing cooling loads in warm climates.

How It Works

When sunlight hits a window, some energy is reflected, some is absorbed, and some passes through. SHGC represents the fraction of solar radiation that enters the building as heat. For example, an SHGC of 0.40 means 40% of the solar heat striking the window enters the interior.

Climate Considerations

In the San Francisco Bay Area, where cooling needs often outweigh heating, lower SHGC values (typically 0.25–0.40) help keep homes comfortable and reduce air conditioning use. Low-E coatings and tinted glass can lower SHGC while still allowing natural light.

Relationship to Other Ratings

SHGC is one of several NFRC ratings used to evaluate window performance. It works together with U-factor (heat loss) to give a complete picture of a window's energy efficiency.