Understanding Solar Heat Gain Coefficient (SHGC)

Solar Heat Gain Coefficient (SHGC) measures the fraction of solar radiation that passes through a window as heat, expressed as a number between 0 and 1. Lower numbers mean less solar heat gets through — the window blocks more of the sun's heat, not just its visible light.

Why orientation changes the ideal number

This is where SHGC gets more nuanced than U-factor. A low SHGC is generally good for south- and west-facing windows in Indiana's hot summers, reducing cooling load. But on north-facing windows — which get little direct sun regardless of season — a very low SHGC provides no meaningful summer benefit and can reduce helpful winter solar warming.

Some homeowners work with their installer to select different SHGC glass packages for different orientations on the same home — a more advanced approach, but a legitimate one if you're optimizing seriously for energy performance.

Typical ranges

Most Low-E replacement windows fall between 0.25 and 0.40 SHGC. For a straightforward, single glass-package approach across the whole home, something in the 0.25–0.32 range is a reasonable middle ground for Indiana's climate.