What is solar heat gain coefficient (SHGC)?
Solar heat gain coefficient (SHGC) is the fraction of incoming solar radiation that passes through a window and becomes heat inside, measured on a scale from 0 to 1.
SHGC quantifies how much solar radiation a window allows through as heat, expressed as a number between 0 and 1. An SHGC of 0.5 means the window admits 50 percent of the sun's heat energy; lower numbers indicate greater rejection of solar heat. This metric matters alongside U-factor, which measures heat loss through conduction, because they address different thermal paths affecting your heating and cooling costs across seasons.
In Connecticut, SHGC takes on particular weight for south and west-facing windows. Summer sun on these exposures drives cooling demand, and a lower SHGC (typically 0.30 to 0.50) reduces the load on air conditioning systems during warm months. Winter solar gain through south-facing windows can help offset heating needs on clear days, so homeowners and window installers often balance SHGC against U-factor: a moderate SHGC on south exposures permits useful winter warmth, while lower SHGC on western walls shields living spaces from afternoon heat gain. North and east-facing windows typically prioritize lower U-factor (better insulation) over SHGC control since they receive minimal direct sun.
Window product labels display SHGC prominently, helping Connecticut homeowners choose units matched to orientation and climate zone. Replacement window providers can help match SHGC ratings to your home's layout and local weather patterns.