SHGC is best described as a ratio where 1 equals the maximum amount of solar heat allowed through a window, and 0 equals the least amount possible allowed through. The NFRC. . The National Fenestration Rating Council (NFRC) is the trusted, independent, nonprofit certification body for the energy performance of windows, doors, and skylights. The SHGC rating assigned to a window. . Replacing old windows with ENERGY STAR certified windows lowers household energy bills by an average of up to 13 percent nationwide when replacing single-pane windows. Lower energy consumption also reduces greenhouse gas emissions from power plants and homes. Simonton 5500 Collection Simonton Madeira Collection Learn. . Solar heat gain coefficient (SHGC) measures a window's ability to control how much of the sun's heat enters the home.
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