SHGC
SHGC (Solar Heat Gain Coefficient) measures the fraction of solar radiation that passes through a window and becomes heat inside the building. SHGC ranges from 0 to 1 — lower SHGC blocks more solar heat (good in cooling-dominated climates), higher SHGC admits more (good for south-facing windows in heating-dominated climates that want passive solar gain). SHGC is an NFRC-rated number that includes glass, frame, and spacer effects.