4 Things to Know About Solar Heat Gain

Buyers consistently rank numerous and well-placed windows among the most appealing features of a home. Windows help a home stay bright and cheery, while also often permitting pleasant views. Yet sometimes windows present disadvantages as well, especially for those who live in especially hot or sunny parts of the country.
By permitting sunlight to enter your home, windows often contribute to unwanted solar heat gain. Unfortunately, many homeowners fail to realize the impact of solar heat gain. If you would like to learn more about how your windows affect the overall efficiency of a home, keep reading. This article outlines four key things to know about solar heat gain.
1. Solar Heat Gain Has a Huge Effect on Energy Efficiency
Anybody who's ever lived through a summer in a hot part of the country knows the huge role that the sun plays in driving up cooling demands. Yet fewer people realize just how much of that effect relates to sunlight coming through your windows. As much as a staggering 87 percent of summertime heat gain comes through your windows and skylights.
Sunlight passing through your window glass has perhaps the largest effect on unwanted heat gain. Yet heat gain also happens as the result of unwanted drafts from windows allowing air to get in — and out — of your home. Solar heat gain stemming from such drafts may make up as much as 25 percent of your energy bills in summer.
2. Manufacturers Quantify Solar Heat Gain as SHGC
Home builders and engineers have long recognized the importance of determining the precise solar energy transmittance of windows. Manufacturers now quantify a window's effect on heat gain by means of the solar heat gain coefficient, or SHGC for short. This number expresses the ratio of transmitted radiation — aka heat — to the overall level of incident radiation.
In other words, SHGC tells you just how much of the sunlight striking a window actually makes it through into your home. A SHGC always falls somewhere on a spectrum between 0 and 1, with higher numbers indicating that more heat passes through a window.
3. SHGC Varies From Window to Window
As you can probably guess, the solar heat gain coefficient varies from window to window. Lower SHGC ratings offer better protection for those in heat-prone areas, while higher ratings may be acceptable for those in colder climates.
For instance, double-glazed windows tend to have an SHGC between 0.42 and 0.55. More efficient triple-glazed windows, by contrast, have an SHGC between 0.33 and 0.47. A window with an SHGC of 0.6 will allow twice as much heat into your home as a window with an SHGC of 0.3.
While higher SHGC windows always block more unwanted heat transmission, they may not be strictly necessary. Windows that receive ample amounts of shade — whether from awnings or trees in your yard — avoid many of the pitfalls of solar heat gain.
4. You Can Reduce Solar Heat Gain From Existing Windows
For older homes, upgrading to more modern windows can drastically improve energy efficiency. Yet even those who cannot afford entirely new windows can reduce solar heat gain through the application of window films. Some window films reduce solar heat gain by absorbing radiation, while others do so by reflecting it away from your home.
Window films also vary in terms of visible light transmittance — in other words, how much light they allow through. By closely considering your needs, you can often find a window film that offers excellent solar heat gain reduction while still allowing optimal levels of light into your home.
In an age of rising energy costs and warming climate, solar heat gain poses a real threat to your bottom line. For more information about how to keep solar heat gain within acceptable limits, please contact the door and window experts at Advantage.