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What is Low-e Glass?

Windows, Low-e Glass

Today’s tip is about low-e glass, (the “E” stands for emissivity) which is being increasingly being specified for commercial windows because low-e glass can help save energy. Introduced in 1979, low-e glass works by preventing the sun’s heat energy from entering a facility through the windows. Low-e glass uses an ultra thin metallic coating on or in the glass to reflect the sun’s rays. There are two types of windows with low-e glass: Standard low-e and solar control low-e.

Windows can come with either standard low-e glass, which has a visible transmittance of about .78 and a solar heat gain coefficient of about .54.

Solar control low-e glass, generally used in hot climates, has the same visible transmittance, but with a solar heat gain coefficient as low as .4 – which is, on balance, a pretty good number. Solar control low-e glass works by blocking certain wavelengths of UV light and IR light. Obviously the low-e coating should be applied to the outside pane of glass.

However, if you are in a cold climate and want to keep heat in the facility, you could use low-e glass on the inner pane of glass.

According to the US Department of Energy, windows with low-e glass cost about 10-15 percent more than traditional windows, but can reduce heat through the windows as much as 30 to 50 percent.

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