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Replacement Window Ratings - What They Mean
Windows are rated in a range of categories which establish their energy efficiency. If you are choosing windows for your house, more emphasis should be placed on various ratings based on the climate the home is located in. For instance, if you are purchasing for replacement windows in Phoenix, Arizona, a sunny and warm climate, the Solar Heat Gain Coefficient is quite likely the most essential rating to take into consideration. Other variables, such as the orientation of a window to the sun and the amount of shade that is present ought to be considered.
The U.S. Government's Energy Star program is intended to make it easier for individuals to identify energy efficient products and practices which will save them money and safeguard the environment. The Energy Star program rates over 60 products, including windows. Energy Star certification makes it convenient for consumers to be certain that they are getting energy efficient replacement windows.
All Energy Star replacement windows are scored in five areas but Energy Star qualification is solely based on the U-Factor and Solar Heat Gain Coefficient. These ratings are also the categories used to calculate if a window qualifies for the IRS Energy Tax Credit.
U-Factor
Calculates the pace of heat transfer and denotes how efficiently a window insulates. The smaller the U-Factor rating, the better a window insulates. The window U-Factor incorporates the thermal characteristics of the frame as well as the glazing.
Solar Heat Gain Coefficient (SHGC)
Determines the solar energy transferred by the window and denotes how well a window blocks heat caused by the sun's energy. The smaller the SHGC, the less solar heat a window transmits.
Visable Transmittance (VT)
Determines the amount of light a window permits through. The higher the Visable Transmittance, the brighter a room will be.
Air Leakage (AL)
Measures the rate at which air passes through joints in a window. Air Leakage is measured in cubic feet of air passing through 1 square foot of window area per minute. The lower the Air Leakage value, the less air that is leaked.
Condensation Resistance
Determines how well a window prevents water build-up. The higher the Condensation Resistance factor, the less condensation build-up a window permits.
Other Replacement Window Ratings
There are a few other ratings that are not included on the NFRC Energy Star label but they are useful and show up on some windows.
Light to Solar Gain
The ratio of Visable Transmittance (see above) to Solar Heat Gain Coefficient (see above) calculates the amount of light that is transmitted without adding heat. A higher number means that more light is transmitted without adding heat.
R-Value
R-Value was created as a way to measure the insulation value of a product. It calculates conductivity and signifies the resistance to heat flow. A high R-Value signifies a better insulated window. The majority windows today are measured using U-Factor (see above).
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