Window Ratings
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The National Fenestration Ratings Council (NFRC) is a non-profit, third-party agency which rates, tests, certifies and labels windows according to their ability to provide thermal insulation and protection from the weather. The NFRC provides these ratings in order to assist consumers compare replacement window performance and are used in the Energy Star program. | The National Fenestration Ratings Council (NFRC) is a non-profit, third-party agency which rates, tests, certifies and labels windows according to their ability to provide thermal insulation and protection from the weather. The NFRC provides these ratings in order to assist consumers compare replacement window performance and are used in the Energy Star program. | ||
− | The NFRC rates a window's U-Factor, its solar heat gain coefficient, its visible transmittance, its air leakage and its light to solar gain but ENERGY STAR windows® are based | + | The NFRC rates a window's U-Factor, its solar heat gain coefficient, its visible transmittance, its air leakage and its light to solar gain. |
+ | but ENERGY STAR windows® are based on a window's U-Factor and SHGF ratings | ||
=== Energy Star Ratings === | === Energy Star 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. | 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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=== U-Factor === | === U-Factor === | ||
− | The U-Factor measurement assesses the rate at which a window is able to conduct non-solar heat. This rating represents an entire window's performance including the window's glazing, frame and spacer material. The lower the U-Factor rating, the more energy efficiency the window provides. | + | The U-Factor measurement assesses the rate at which a window is able to conduct non-solar heat. This rating, also called the U-Factor, represents an entire window's performance including the window's glazing, frame and spacer material. The lower the U-Factor rating, the more energy efficiency the window provides. |
=== Center of Glass U-Factor === | === Center of Glass U-Factor === | ||
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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 === | ||
− | + | The rate that air infiltrates into a room from the area that surrounds a window is the window's Air Leakage rating. Window spacers, sealants and other weatherstripping products impact on a window's air leakage. A low air leakage rating indicates that the window has a low percentage of air leakage. | |
=== 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 === |