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Building Science by Norman Aceron Garcia

Low-E windows

by Norman Aceron Garcia

Low E WindowsA low-emissivity, also known as low-E, coating is a microscopically thin metallic film applied on the glazing that functions like a mirror and radiates heat back into the interior space during the heating season (winter), and back to the exterior environment during the cooling season (summer). This almost invisible metallic oxide layer helps to minimize heat transfer through windows, thereby reducing energy loss by 30 to 50 per cent.

A low-e coating gives a double-pane window almost the same energy performance as a window with an uncoated triple-pane, but at a lesser cost. Most window manufacturers offer low-E coatings as a standard feature in their windows. The low-E coatings are usually installed on multi-pane windows that are filled with argon, an inert, non-toxic, colourless and odourless gas that has higher heat flow resistance than air.

In colder, heating-dominated climates such as Manitoba, the low-E coating is applied to the inner layer of the glazing to help keep the heat in. About 40 to 70 per cent of the infrared portion of the light spectrum is reflected, while at the same time all visible light is allowed to pass through.

There are two types of low-E coatings: pyrolytic and sputtered. A pyrolytic coating, also called a hard-coat low-E coating, is made of tin oxide and additives installed directly onto the glazing surface during the production process while it’s still hot. This production method results in a sturdy baked-on surface layer on the glazing. This type of coating is typically applied on insulated glazing units where the low-E coating is within the sealed air space.

On the other hand, sputtered coatings typically comprise of three primary coatings with at least one layer of metal placed on a plastic or glass film. Sputtered coatings must be covered from humidity and contact, which is why they are also commonly called soft-coat low-E coatings. Like pyrolytic coatings, these are usually installed inside the sealed air spaces of multi-pane windows and can be installed in suspended films and to retrofit windows.

Energy-conscious consumers can benefit from understanding the advantages of low-E windows over conventional windows. Selecting windows with a low-E coating can significantly reduce energy costs, thereby decreasing our dependence on fossil fuels.

Norman Aceron Garcia, P.Eng. is an accredited professional in Leadership in Energy and Environmental Design specializing in Building Design + Construction. In 2015, Norman founded Mr. Peg Property Inspections, a social enterprise that advocates green building design and climate change adaptation strategies.

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