You might redesign your house in any number of ways, but you're pretty unlikely to design it without windows. Still, as much as we love the light and views from windows, drafts and heat loss from inefficient glass plague homeowner. Newer window designs provide better insulation and even help heat your home, saving you money and energy. Energy-efficient replacement windows are more a luxury than a necessity, however, and you can save energy in other ways as well.
A window's U-factor is the rate at which it conducts non-solar heat. For example, if your heat your home at night, any heat lost through the windows is measured by the windows' U-factor. Traditionally, a window's U-factor referred to just the glass or glazing. Windows rated by the National Fenestration Rating Council, however, also include ratings of the frames and spacer material. Any part of your window can contribute to heat loss. (See References 1) For most of the United States, choose windows with a U-factor of 0.30 to 0.35, to help keep heat indoors during cold weather. People living in the extreme South, however, should seek out windows with a U-factor of around 0.60. (See References 2)
Solar Heat Gain Coefficient
Solar radiation passes through your windows when the sun shines. The windows absorb this radiation, and then transmit it into your home as heat. If your window has a low Solar Heat Gain Coefficient, it transmits less heat from solar radiation and can help keep your home cooler during hot months. (See References 1) People living in northern areas should look for windows with an SHGC of 0.35 to 0.40. People in southern and south-central areas should look for an SHGC of 0.27 to 0.30. (See References 2)
Unless you've purposely opened windows, they should not let air pass through. Airflow can cause significant problems, accounting for up to 10 percent of your home's energy use (see References 3, page 9). To keep your heated or cooled air from escaping, you need a window frame, sash and seal that close tightly without drafts. If your current windows don't seal correctly, you should either replace them or seal them off with plastic covering during extreme weather periods.
New windows are expensive and you may be able to attain significant energy savings by improving the windows you already own. The U.S. Department of Energy recommends adding storm windows, caulking and weatherstripping to reduce air leakage. You can also use window treatments or curtains to reduce solar heat gain inside your home. (See References 4) If you are remodeling or designing a home, consider more than just the windows. You can save significant amounts of energy by employing passive solar techniques, letting the sun heat and cool your home naturally (see References 5).
- 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: Selecting Windows for Energy Efficiency
- 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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