What is the Solar Heat Gain Coefficient?

Measuring how much solar radiation passes through a window into a home

The SHGC of a window is a measurement of the heat transmitted through a window that is absorbed and released into a home. SHGC is expressed as a number between 0 to 1.

“0” being the least amount of heat being allowed through a window
“1” being the most amount of heat being allowed through a window

Solar gain enters the home through:

1. “Direct” solar radiation from the sun
2. “Absorbed” solar radiation heat that is transferred through the glazing and framing materials by conduction, convection, and radiation.

Solar heat gain can warm a room during the day in the winter (providing free heating), but it can also cause overheating in the summer. Keep in mind, there is no solar gain at night.

Window & glass manufacturers are able to control the intended solar gain or decreased loss through various levels of tinting or coatings that can be applied to the glass.

Finding the right balance of solar heat gain with an appropriate SHGC value depends upon:

• Climate
• Window orientation (facing north, south, east or west)
• Shading (buildings, trees, blinds…)

High solar gain windows can be controlled in the summer with the use of external or internal shading devices.

SHGC Summary for Ottawa:

• The larger the SHGC number, the greater the solar gain (more heat)
• The smaller the SHGC number, the lower the solar gain (less heat)