The Solar Heat Gain Coefficient (SHGC) measures how much solar radiation is admitted through a window or glass wall. It represents the solar heat gain through the glass, relative to the incident solar radiation.

Shading Coefficient is an older measure of solar radiation, and is the inverse of SHGC. The shading coefficient is the ratio of solar energy that passes through the glass, relative to a piece of 1/8” clear glass (which has a shading coefficient of 1.0).

The optimal amount of solar heat gain depends on the climate. A higher SHGC is generally preferred in colder, heating-dominated climates, such as Northern USA and Canada. A high SHGC it is more effective at collecting solar heat. During the longer winter heating season, the extra solar radiation becomes “free” heat. A lower SHGC is generally preferred in warmer, air-conditioning-dominated climates, such as Southern USA and Mexico. A low SHGC blocks heat from the sun. With a long air-conditioning season, reducing solar heat gain and cooling loads is a priority.