The Solar Heat Gain Coefficient of a dpuble glazed window.

What Is Solar Heat Gain Coefficient (SHGC)?

The Solar Heat Gain Coefficient for windows (expressed as SHGCw) measures how readily heat from direct sunlight flows through a window system. The SHGC is the fraction of incident solar radiation admitted through a window, directly transmitted as well as absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1.

The lower a window’s SHGC, the less solar heat it transmits.

It’s wise to remember that the SHGC rating is on the whole window- including the frame. So expect that a standard aluminium frame will not perform well. To get the best SHGC rating, the window frames should be made of timber, uPVC, or aluminium with a thermal break.

SHGC ratings are produced by tests under the Window Energy Rating Scheme (WERS). WERS provides a list of window manufacturers, and their WERS approved windows. The Ratings include the SHGC figures.

Source: The Australian Window Association. Heat transfer mechanisms.

Information on SHGC, u-Factor, and Visible Light Transmittance, from a US retailer.


In temperate and cool temperate climates such as Sydney, Perth, Melbourne, Adelaide and Hobart, northerly glazing should have a high SHGC. This is standard passive solar practice for temperate climates. Northerly windows are the home’s solar collectors. However, these windows should also have fixed or adjustable shading designed to shade as little of the glass in winter as possible while shading as much as possible in summer. Source: Glazing


The Solar Heat Gain Coefficient is just one of the measures that tells us how well a double glazed window performs. You should also check up on u-Values, and Visible Light Transmittance.
 Posted on : December 28, 2017