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How Replacement Window Energy Performance is Rated

Last updated 6 years ago

Replacement windows are an investment in your home’s appearance and value. Besides boosting curb appeal, replacement windows can make your home more energy-efficient, which can save you money now and also add to its potential resale price. Not all windows have the same efficiency ratings, however. Window energy performance is measured by calculating several different factors:

Visible Transmittance (VT)
This rating tells you how much visible light your window will let into your home, with a higher value indicating more light. Although the visible transmittance doesn’t affect how well the window insulates or conducts heat, it is still a useful number for determining energy efficiency. Windows with a high VT can help light your home naturally and save you electricity during the day.

Solar Heat Gain Coefficient (SHGC)
Measured on a scale from 0 to 1, the solar heat gain coefficient indicates how much the window will allow sunlight to heat your home. The lower the number, the less heat the window allows to pass through. Windows on different sides of your home receive varying amounts of sun at different times of year, so not all of your windows should have the same SHGC.

Air Leakage (AL)
Because homeowners often use air conditioning and heating to maintain comfortable inside temperatures when the weather is extreme outside, air leakage around windows can increase energy consumption. This is because the HVAC system will have to run longer to counteract the effects of outside air on inside temperatures. Energy-efficient windows have low AL ratings, but it’s also important to have professionals install and seal the windows correctly to minimize air leakage.

The U-Factor measures how much the window assembly resists heat transfer. Quality replacement windows should help insulate your home. To prevent heat from escaping your home in the winter and entering it in the summer, choose windows with a low U-Factor.

When it’s time to upgrade your windows, contact Progressive Insulation & Windows of Southern California. Call us today at (818) 709-0988 to discuss installing energy-efficient windows in your home.


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