Types of Window Glazing
When selecting windows for your new home or replacing windows in your existing home, it's important to choose window glazing that will be energy efficient. The type of glazing you choose will depend on several factors, including climate and window orientation. There are several types of window and glazing available.
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Terms
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Before exploring the window glazing options, there are a few terms to be defined. First, many of these glazing types are used for insulation, which means the window consists of two or more panes of glass sealed along the edges with a space between them to resist heat flow. The space between panes can contain air or gas.
U-factor refers to the rate at which the window allows heat flow. The lower this number is, the more energy-efficient the window.
Finally, the solar heat gain coefficient, or SHGC, is the amount of solar radiation transmitted through the window and released into the home. A low SHGC provides more shading, while a high SHGC allows more heat to pass through.
Heat-Absorbing
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Heat-absorbing window glazing is tinted to absorb much of the solar radiation that passes through the window. Different tints have different effects; blue and green tints allow more visible light and reduce heat transfer. Gray and bronze tints reduce both light and heat.
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Low-Emissivity
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Low-E coating is used with insulated glazing and can reduce energy loss by up to 50 percent. It is a thin metallic oxide layer coating the surface of one or more panes of glass. It lowers the U-factor by reducing the heat transfer from a warmer pane of glass to a cooler one. The window's use determines where the coating is applied; to keep heat out, the low-emissivity coating should be on the outside pane, and to keep heat in the Low-E coating should be on the inside pane.
Spectrally Selective
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Spectrally selective window glazing is a type of low-emissivity coating which filters out up to 70 percent of the infrared radiation (heat) that usually passes through the window, while still letting the full amount of light through. This results in a low U-factor and SHGC without increasing the need for artificial light.
Reflective
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Reflective coatings consist of thin metallic layers and come in a variety of colors. They work by blocking solar radiation, reducing visible light and glare, and lowering the SHGC of the window.
While reflective glazing is useful in hot climates to reduce cooling energy use, the extra electrical load for lighting may reduce the overall benefit.
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