Definition of Solar Heat Gain Coefficient

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When remodeling a home, be aware of energy codes and regulations before diving into an extensive project. When installing windows, pay attention to the solar heat gain coefficient (SHGC), which measures how well a window blocks heat from the sun. According to the U.S. Department of Energy, "the SHGC is the fraction of the heat from the sun that enters through a window."

SHGC Specifications

  • According to the U.S. Department of Energy, the SHGC is expressed as a number between zero and one, with a lower number expressing less solar heat transmission. The SHGC of a window is found on the National Fenestration Rating Council (NFRC) label, attached by the manufacturer prior to sale.

IECC Compliance

  • If all of your windows have a SHGC of .40 or less, then simply stating this on your compliance forms is sufficient enough to comply with the International Energy Conservation Code (IECC). If your windows do not meet the .40 or less requirement, use the REScheck software available at www.energycodes.gov. The REScheck software calculates specific properties of your windows including: SHGC, orientation, and overhang projection factors.

Benefits

  • Understanding the SHGC of your windows can help reduce energy costs for heating and cooling purposes. EfficientWindows.org explains that northern/colder climates generally require windows with higher SHGCs, between .30 and .60, offsetting the amount of energy needed for heating purposes. Warmer climates usually require windows with lower SHGCs, typically .40 or lower, and decreases home cooling costs.

Other Window Properties

  • In addition to a window's SHGC, there are other important factors to consider in terms of energy conservation, including the u-factor, visible transmittance, and air leakage. U-factor measures rate of heat loss; visible transmittance (VT) is an optical property that indicates the amount of visible light transmitted; and air leakage determines heat gain and loss, due to cracks within the window framing. These properties, as well as the SHGC, are interrelated and determine a window's energy efficiency.

Expert Insight

  • When renovating an older home, replace all outdated windows. Older houses usually have deterioration and/or swelling of wood framing, especially around windows. In colder climates, this causes unwanted drafts, creating heat loss; in warmer climates, cooling the home is more challenging. As a result, the cost to cool or heat your home will be significantly higher. This can be remedied by replacing old windows with modern models to drastically reduce energy costs for your home.

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