SHGC

Solar Heat Gain Coefficient, or SHGC, is a measure used in glazing and fenestration to indicate how much solar radiation passes through a window or glazing system and contributes to interior heat. It represents the fraction of incident solar energy that ultimately becomes heat inside the building, either by direct transmission or by absorption and subsequent release of heat inside.

SHGC is a dimensionless value between 0 and 1. A lower SHGC means less solar heat gain from the sun, while a higher SHGC indicates greater solar heat contribution. SHGC is influenced by the glazing’s materials, coatings, the number of panes, gas fills, and spacer technology. It does not directly measure daylight or visible transmittance, though there is often some correlation.

In practice, SHGC is determined under standardized test conditions and is often published as part of fenestration ratings. In the United States, ratings are commonly provided by the National Fenestration Rating Council (NFRC). In Europe and other regions, SHGC-equivalent values are described as g-values or through regional rating schemes. Shading devices, frame design, and installation details can modify the effective SHGC in a building, even if the window’s rated value remains fixed.

Typical SHGC values vary by product type. Clear double glazing might have SHGC around 0.60–0.80, while low-emissivity (low-E) coatings or spectrally selective glazing can reduce SHGC to roughly 0.25–0.40. Triple glazing can further influence SHGC, depending on coatings and gas fills. SHGC is used alongside the U-factor in energy codes and performance models to optimize thermal comfort and energy use in different climates.