Window Ratings
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The [[Energy Star Windows|Energy Star]] certification provides assurance that a window is able to limit heat transfer and control the amount of solar gain that enters into a home through the window. Energy Star qualified windows lower energy consumption and reduce greenhouse gas emissions through their ability to control weather penetration and heat transfer. Energy Star windows are certified based on the ratings of the National Fenestration Ratings Council but they do not include all the NFRC's component ratings. | The [[Energy Star Windows|Energy Star]] certification provides assurance that a window is able to limit heat transfer and control the amount of solar gain that enters into a home through the window. Energy Star qualified windows lower energy consumption and reduce greenhouse gas emissions through their ability to control weather penetration and heat transfer. Energy Star windows are certified based on the ratings of the National Fenestration Ratings Council but they do not include all the NFRC's component ratings. | ||
− | Windows which receive the Energy Star label are assessed according to the NFRC's ratings for U-Factor and solar heat gain coefficient but do not take into account the additional ratings -- Air Leakage, Visible Transmittance and Light to Solar Gain. ENERGY STAR® windows are accepted by many governments as windows products that make the buyer eligible for tax credits and rebates | + | Windows which receive the Energy Star label are assessed according to the NFRC's ratings for U-Factor and solar heat gain coefficient but do not take into account the additional ratings -- Air Leakage, Visible Transmittance and Light to Solar Gain. ENERGY STAR® windows are accepted by many governments as windows products that make the buyer eligible for tax credits and rebates |
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== Rating Component == | == Rating Component == | ||
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=== Solar Heat Gain Coefficient === | === Solar Heat Gain Coefficient === | ||
− | The solar heat gain coefficient (SHGF) relates to a percentage of solar radiation which is either absorbed or directly transmitted through a window, and is subsequently released, creating warmth in the room. When less solar heat is transmitted there is greater shading ability which results in a lower solar heat gain coefficient. Windows with high SHGF ratings transmit more solar heat gain during the winter months while windows with a low SHGF rating reduce cooling loads more effectively during the summer months when they block heat from the sun. | + | The solar heat gain coefficient (SHGF) relates to a percentage of solar radiation which is either absorbed or directly transmitted through a window, and is subsequently released, creating warmth in the room. When less solar heat is transmitted there is greater shading ability which results in a lower solar heat gain coefficient. Windows with high SHGF ratings transmit more solar heat gain during the winter months while windows with a low SHGF rating reduce cooling loads more effectively during the summer months when they block heat from the sun. The need for a high or low SHGF is dependent on the climate in which the windows are to be installed. |
=== Air Leakage === | === Air Leakage === | ||
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=== Light-to-Solar Gain === | === Light-to-Solar Gain === | ||
− | Light-to-Solar Gain (LSG) | + | The rating for Light-to-Solar Gain (LSG) indicates the ratio between the visible transmittance and the solar heat gain coefficient. The measurement for light to solar gain assesses the relative efficiency of different types of glazing as daylight is transmitted to gauge how well the glass blocks heat gains. A high LSG rating will indicate that a higher ratio of light is transmitted without significantly adding higher amounts of heat. |
=== Visible Transmittance === | === Visible Transmittance === |