Windows are an essential part of any home, but they come at a cost. In exchange for light and beautiful views, homeowners experience significant energy loss and drafts. Newer window designs solve these problems with better design and insulation that can even help heat your home and save energy. Replacing your windows with energy-efficient models can be expensive, however, and you may be able to improve the windows you have at a much lower cost.
One major source of heat loss through your windows has nothing to do with the type of window you use. Small leaks around the frame, sash and seal can account for up to 10 percent of your home's energy usage (see References 1, p. 9). To keep heated or cooled air from escaping, caulk and plug any leaks, install storm windows or cover windows with plastic sheeting. If your windows are old, you may need to replace them with newer, tighter-sealing models. Unless you've opened them on purpose, your windows should not be letting air pass through.
On cold days, your windows may be cool to the touch due to their U-factor --- the rate at which the glass conducts nonsolar heat. This type of heat transfer can be reduced by using double- or triple-paned windows, but always check the U-factor rating before buying. The National Fenestration Rating Council rates windows on the efficiency of not only the glass and glazing, but also the frames and spacer materials (see References 2).
Solar Heat Gain Coefficient (SHGC)
When the sun shines on your windows, the glass absorbs the radiation and transfers it into your house as heat. Windows with a low solar heat gain coefficient --- SHGC --- will transmit less heat, keeping your home cooler in hot weather (see References 2).
When purchasing new windows, look for products that have been rated by Energy Star or the National Fenestration Rating Council. These products are guaranteed to help your home save energy, providing you install the windows correctly. In most of the United States, choose windows with a U-factor of 0.30 to 0.35. This helps keep heat indoors during cold months. In the extreme South, look for a U-factor of around 0.60 to keep you cool in hot weather. (See References 3) In the northern United States, choose windows with an SHGC of 0.35 to 0.40. In southern and south-central areas, look for windows with an SHGC of 0.27 to 0.30. (See References 3)
New windows can be costly, so first see if you can raise your home's energy efficiency by improving the windows you already have. The U.S. Department of Energy recommends caulking and weatherstripping any leaks and adding storm windows in winter months to reduce airflow from cold winds. You can also reduce solar heat gain inside your home by installing window treatments or curtains. (See References 4) If you're designing or remodeling, consider more than just the windows to improve energy efficiency. Passive solar techniques can save you significant amounts of energy by letting the sun heat and cool your home naturally (see References 5).
- U.S. Department of Energy: Selecting Windows for Energy Efficiency
- U.S. Department of Energy: Energy Savers: Energy Performance Ratings for Windows, Doors, and Skylights
- Energy Star: What Makes it Energy Star?
- U.S. Department of Energy: Improving the Energy Efficiency of Existing Windows
- U.S. Department of Energy: Passive Solar Design for the Home; February 2001
An award-winning blogger, Jessica Blue has been promoting sustainability, natural health and a do-it-yourself attitude since graduating University of California, Berkeley in 2000. Her work, seen in a wide variety of publications, advocates an environmentally-responsible and healthy lifestyle.
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