This measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted, and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. A window with an SHGC rating of 0.70 will allow 70% of the solar heat to pass through it. The lower a window's solar heat gain coefficient, the less solar heat it transmits. A high solar gain window will let in solar heat and trap it, increasing cooling load in the summer. In Florida, where low SHGC is the most important consideration in selecting windows, select those with a whole window SHGC of 0.40 or less. Be sure to compare NFRC labels or purchase ENERGY STAR® windows for thesouthern climate.

Additional Resources

UF IFAS Energy Efficient Homes: Windows and Skylights - http://edis.ifas.ufl.edu/FY1045

Building a Safer Florida, Inc., University of Florida's Program for Resource Efficient Communities, and the Florida Department of Community Affairs. May 2006. Window Systems http://www.dca.state.fl.us/fbc/publications/Fact_Sheets_0307/WindowSystems061506revised.pdf  

Efficient Windows Collaborative. September 2007. Fact Sheet: Selecting Energy Efficient Windows in Florida. http://www.efficientwindows.org/factsheets/florida.pdf