What you need to know about solar heat gain

Posted by Woodrow Aames ~ April 22, 2012

Controlling solar heat gain is one of the best ways to fight back against rising utility bills and protect your investment. Here's all you need to know from the start: the solar heat gain coefficient (SHGC) measures how well your windows block the amount of heat from the sun that enters your home. The SHGC is expressed on windows in the showroom as a number between zero and one, with the lowest number meaning the greatest protection.

The National Fenestration Rating Council (NFRC) was created to set universal benchmarks for SHGC, and its labels appear as the sticker on window products. Awnings, well-positioned shade trees and blinds can help quite a lot. But buying replacement windows with certified NFRC labels indicating excellent SHGC ratings are the most efficient way to curb unwanted summer heat.

Percentages matter in window ratings and energy efficiency

The SHGC rating is expressed in a fraction. Hence, a SHGC of .5 means the window transmits 50 percent of the sun's heat that streams at it directly into your home. Use the NFRC rating labels as an evaluation tool when comparing replacement windows.

A main consideration is whether to buy spectrally selective glass for your windows. Coated or tinted glass (known as Low-E glass) is becoming more common among the energy efficient windows in the marketplace. The NFRC maintains an online directory of certified window products. Low-E coatings have been found to reduce between 40 and 70 percent of solar heat gain.

You should shop by region, plugging in your local climate conditions in your product evaluations. For example, you may want a high number SHGC in cold northern states where your priorities are for conserving heat indoors while inviting warm rays from the sun into your home during winter. In hot southern climes, a low SHGC can make all the difference in your summer cooling bills.

The Department of Energy reports that you can reduce your cooling requirements in hot climates by more than 40 percent by combining spectrally selective coatings with advanced window glazing and coatings. Energy-efficient windows, installed correctly, save money.

Other heat gain factors

Typically, you'll find the use of awnings more prevalent where summer sun is intense. You'll still have a good view outside and you can roll up or remove canvas awnings come winter. Some homeowners use solar curtains made from polyethylene or Low-E shades that also screen invasive heat.

Remember, too, that your most-important concerns should focus on south-facing windows. You may not find it necessary to surround your entire home with high-performance windows. And don't forget to consider the SHGC for your skylights!

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