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We take it for granted that “heat efficient windows” are a good thing. But how do they really help us? There are two primary factors in rating heat efficient windows. U-factor measures the window’s ability to retain indoor warmth (important in winter), and solar heat gain coefficient (SHGC) measures the window’s ability to block the sun’s heat (important in summer). For both ratings, the smaller the rating number, the better. A recent report from the University of Minnesota Center for Sustainable Building Research discussed selecting energy efficient windows for New York. The report outlined some important benefits of heat efficient windows, including: Comfort Many specific features can help lower a window’s U-factor, which means more retained indoor heat. Low-E coatings and gas-filled double- or even triple-pane windows, insulating spacers and frames all help lower U-factor. Low U-factor also helps keep the windows themselves from getting cold, a problem that can cause chilly drafts. To fend off summer heat, many low-E coatings also reduce solar heat gain. This means sunny indoor seating or working areas won’t feel so warm in the summer. More daylight, better view Glass coatings such as tints and films have been around for some time, but the older types often reduced visible light as well as heat. Modern low-E coatings retain window clarity while substantially reducing solar heat gain, so you can enjoy the efficiencies as well as crystal-clear views. Reduced condensation Condensation is caused by excessive temperature contrast between the window and indoor air. Frame materials (include spacers and glazing) that don’t conduct heat help lower this differential, so condensation is less likely to form. Furniture protection Ultraviolet light (UV) can seriously damage both wood and fabrics over time. Glass coatings that reduce U-factor and SHGC also reflect UV light and other solar radiation, so your wood furniture, upholstery and draperies will fade less and last longer. Year-round cost savings More retained heat in winter lowers heating bills. Very low U-factor may even improve your indoor comfort so much, you don’t need (or don’t need to use) heat outlets near your windows. Less solar heat in summer reduces the need for air conditioning, which saves energy and could enable you to use smaller cooling equipment, saving more money. Sometimes there are trade-offs between U-factor and SHGC, so be sure to weigh all the factors in deciding which heat efficient windows are best for your home.
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