Solar heat gain coefficient (SHGC)

Solar heat gain coefficient, usually written SHGC, is a rating from 0 to 1 that tells you how much of the sun's heat gets through a glazed opening. A value of 0 means no solar heat passes through, and a value of 1 means all of it does. The rating covers heat that comes straight through the glass and heat the glass absorbs and then releases into the room. It does not measure visible light, which is a separate rating.

The number matters most in a skylight because a skylight sits at a steep angle to the sun for much of the day. That exposure lets in more heat than a vertical window of the same size. In Citrus County, where summers are long and cloud-free stretches are common, a skylight with a high SHGC can push indoor temperatures up and keep an air conditioner running harder through the afternoon. A lower SHGC cuts that load, which is why the rating often comes up when homeowners compare glazing options with local skylight installers.

SHGC is one of several ratings printed on the National Fenestration Rating Council label, along with U-factor, which measures heat loss, and visible transmittance. Florida homes mostly need to watch SHGC, since heat coming in is the bigger issue than heat leaving in winter. Glazing coatings, tints, and laminated glass are the usual ways manufacturers lower the number, and the exact value depends on the product, not on the skylight style alone.

If you are looking for skylight contractors who work in the county, you can browse the skylight replacement providers listed in this directory.