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Windows There is good brief information below or See more information about windows (this is a PDF file) (Note: This article appeared in the local section of the Texas Co-Op Power magazine August 2006 edition) Bandera Electric Cooperative, Inc. wants you to get the most from your energy dollar. A good way to save money on your monthly energy bill is to spend a little to make your home more efficient. One area to consider is your windows. You need to know that in recent years, windows have undergone a technological revolution! Because of the many changes in how windows are made a rating system has been developed to help make window shopping a little easier. One key factor is clear – installing high performance windows now will prevent later regrets. Some of the benefits of high performance windows include: cooling and heating season savings; improved comfort; less moisture condensation; improved daylight use; less sun related fabric and furniture fading; and lower mechanical equipment cost. New energy efficient windows are well worth considering whether you are remodeling an existing home or building a new home. How do you know if a window is going to be right for you? A window with an Energy Star® rating for the climate where you live is a quick way to help gage a product’s quality. But, even Energy Star rated windows can vary in cost and delivered performance. The National Fenestration Rating Council (NFRC) has established a rating system based on four factors that affect the overall efficiency of a window. The four-factor NFRC rating makes product comparison easier. For energy efficiency the U-Factor and Solar Heat Gain Coefficient numbers are most important.
The rated heat loss is indicated in terms of the U-factor (U-value) of a window assembly. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value. In our area the U-factor should be 0.40 or less. But this factor is not as important from an energy efficiency stand point for our area as is the Solar Heat Gain Coefficient (SHGC) rating. Solar Heat Gain Coefficient (SHGC) A low SHGC is the most important window assembly property in warm climates. The SHGC is the fraction of incident solar radiation admitted through a window. The lower a window’s solar heat gain coefficient the less solar heat it transmits. The SHGC rating should be 0.40 or less for windows purchased anywhere in Texas. Visible Transmittance (VT) The visible transmittance (VT) is an optical property that indicates the amount of visible light transmitted. Typically the rating number is between 0.30 and 0.80. The higher the VT number the more light is transmitted. This factor is more related to how much light you need in an area than it is to energy efficiency. Air Leakage (AL) Heat loss and gain occur by air flowing through cracks in the window assembly. The lower the AL number the less air will pass through the window assembly. Window assemblies should have a 0.30 or less AL rating. Leaky windows can impact your energy use, however, it is not as important to overall performance in our area as is U-factor and SHGC. Area Specific Windows The proper rating for windows varies greatly from state to state. A perfect window unit for Texas would be a terrible choice in Montana. If you are looking at windows be sure they are rated for the climate where you live. The construction of a good quality window unit includes a double pane glass always; low-E coating (low solar gain); often argon gas filled and a vinyl and wood frame (or aluminum frame with thermal break) construction. Look for Energy Star® rated windows to get the most energy savings. A study comparing Energy Star vs. Single-Pane windows was done by the U.S. Department of Energy in 2005. In Texas the new replacement windows would have saved over $200 per year in energy costs. The study was based on regional average annual energy use for a 2,000 square feet, single story, detached house with 300 square feet of window area, gas heat and electric air conditioning. There are a number of options when it comes to windows and selecting the right unit is a very important choice. There are good architects, building engineers, builders and building supply specialists who can help you make a wise choice. Internet users will find a number of resources such as |
Bandera Electric Cooperative, Inc., P. O.
Box 667, Bandera Texas 78003, 1-866-BANDERA
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U-Factor