Nowadays, windows are more than just sources of natural light and relaxing outdoor views. They’re also an excellent way to upgrade your home’s energy efficiency, a major theme that’s been trending in the fenestration industry for a long time now.
Window solar heat gain coefficient ratings are one of the most crucial factors to consider. In this article, we talk about why SHGC matters and how most energy efficiency organizations measure it.
Solar heat gain coefficient indicates the fraction of solar radiation transmitted or absorbed through a window glazing and released into the room afterwards. SHGC ratings are commonly used to measure how well fenestration products, including windows, doors, and skylights, can block the sun.
Understanding solar heat gain coefficient is important because it affects your living space in many ways. Aside from achieving optimal indoor temperatures, it can also prevent exposure to the sun’s UV rays, reducing risks of skin cancer in humans and cause colour fading in furniture and interiors.
Windows with a lower SHGC rating have less solar heat transmission and better shading capability. These types of windows effectively block the sun, lessening the need for cooling, which can be of greater benefit to homeowners living where there’s a longer summer season.
On the other hand, windows with a higher SHGC rating collect more solar heat, keeping your home warm and cozy during cold winter months while reducing your heating expenses.
According to The National Fenestration Rating Council (NFRC), SHGC ratings factor in the total solar energy transmittance of a window or door as a whole, factoring in the glass, frame material, sash, divided lite bars, and screens.
To get the bigger picture of how SHGC works and is measured, consider that when the sun hits your windows…
|Solar heat gain coefficient = portion of solar energy transmitted + portion of absorbed solar energy that is emitted inside|
Solar heat gain coefficients are expressed as decimals from 0.00 to 1.00. This is only the theoretical range. In real life, values of SHGC for windows are never a perfect 0.00 (no solar radiation gets through) or 1.00 (all the solar radiation is absorbed).
Most organizations that test for the SHGC either use simulation models or manually record the heat flow through a window by using a calorimeter.
Fortunately, buyers do not need to calculate SHGC themselves when shopping for windows, thanks to energy performance labels by the NRFC and CSA.
SHGC ratings can be easily spotted in most energy performance labels in Canada along with other energy efficiency metrics like:
What makes SHGC so unique from the rest is that it’s the only one that can also give homeowners a glimpse of the amount of solar radiation absorbed by windows. On the other hand, other energy performance metrics tell you more about the insulation properties.
High or low, there is generally no good or bad SHGC rating as it all depends on several factors that are specific to your property. These include:
Now that you know the importance of the solar heat gain coefficient, those decimal numbers on energy performance labels will never look the same again. Ready to shop for energy-efficient windows? Check out our actively updated list of trusted window companies today.