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Energy Efficient Windows

Q: I'm thinking about replacing the windows in my home. I have heard about Low-E glazed windows. How will they help the energy efficiency of my home?

A: The REMC gets several questions regarding the efficiency of low-e glazed windows. Many folks want to know what all the ratings mean, and if using low-E glazed windows can significantly lower their energy bills and is it worth the extra up front expense.

Energy efficient construction depends heavily on cutting down on air infiltration, so the kind of windows you use as well as how well you caulk and seal around them are two major factors to consider when building or remodeling. You should also realize that the extra money and time you invest in windows will have a definite payoff by lowering your energy bills if the rest of the structure is properly constructed.

When you are ready to shop for windows there are three important things to look for: Low-E coating, a U-factor lower than .4 and an SHGC rating of .4 or less. Low-E coating does not always come standard on windows and is sometimes an option you have to order special. This coating cuts down on unwanted heat gain and loss and also reduces the effects of fading on carpets, furniture and other household items due to sun exposure.

U-Factor is a measurement of the rate of non-solar heat loss or gain through a window and SHGC (Solar Heat Gain Coefficient) is a representation of the solar radiation admitted through a window or skylight, both directly transmitted. Both are expressed as a number between 0 and 1 and on a good window should be .4 or less. The lower a window's solar heat-gain coefficient, the less solar heat it transmits. (These two ratings are always clearly marked on the windows with a sticker.) Many times you will also see a VT rating, which is the visible light transmitted through the window.

Another common question is "What brand of window is the best?" Research has shown the brand of window is far less important than finding windows that have Low-E coating, and .4 or lower U-factor and SHGC ratings.

Many energy efficiency experts also recommend the area of windows in your house should only be equal to about 12% of your floor area. In this part of the country we tend to put more than that amount of windows in new houses. Often, the number of windows is not as important as the quality of windows and installation.

Site orientation is also another low-cost factor that can play a part in keeping your home comfortable. If you are thinking about building, consider keeping the majority of windows on the south side of the house. East and west sides get large amounts of sun year round making it more difficult to keep the home cool, while the north side of the home bears the full brunt of harsh weather in the winter, therefore putting more load on your heating system.

Contact Bob Geswein, REMC Energy Efficiency Specialist at 738-4115 or 923-9819 for more information about Low-E glazed windows and other energy saving stratagies.


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