Low-E Glass
Low-E glass, or low emissivity glass usually involves a specially designed coating of metallic oxides that are applied to the surfaces of insulated glass. The coating radiates heat from within the home back inside during the winter while heat from outside is reflected away in the summer. Low-E glass coatings are primarily used to reduce the U-Factor of the insulated glass unit in a window.
Not all Low-E glass is created equal. The Low-E coating can be applied to just one or many of the insulated glass surfaces and according to The U.S Department of Energy "Window manufacturers apply Low-E coatings in either soft or hard coats. Soft Low-E coatings degrade when exposed to air and moisture, are easily damaged, and have a limited shelf life. Therefore, manufacturers carefully apply them in insulated multiple-pane windows. Hard Low-E coatings, on the other hand, are more durable and can be used in add-on (retrofit) applications. The energy performance of hard-coat, Low-E films is slightly poorer than that of soft-coat films."
Also according to The U.S Department of Energy "Windows manufactured with Low-E coatings typically cost about 10%–15% more than regular windows, but they reduce energy loss by as much as 30%–50%."
There are different types of Low-E coatings that have been designed to allow for high solar gain, moderate solar gain, or low solar gain.
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