Low E Windows

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Low E Windows
Low E Windows Windows
Other Names:
Low E Replacement Windows, Low Emissivity Windows
Windows with a Low E coating consisting of a thin layer of oxidized metal to insulate it's glazing.

Low E coatings (Low Emissivity) on glass or glazing controls heat transfer through windows by providing insulated glazing. A Low E coating is a metallic oxide layer which is virtually invisible. It is coated directly onto the surface of a glass pane.

Low E coatings reduce the U-factor of a window by suppressing radiative heat flow. Low E coatings reduce the infrared radiation from the warmer pane of glass to the cooler pane which lowers the window's heat transfer. Manufacturers coat a glass surface with a low-emittance material and then face that coating inward between the glass layers. This process blocks a significant amount of radiant heat transfer which lowers the total heat flow that can enter through a window. Low-E coatings are transparent to visible light.


[edit] Considerations

Homeowners have many considerations when deciding whether to include a Low E coating on their replacement windows.

[edit] Advantages

Replacement windows which are manufactured with Low-E coatings typically cost between ten and fifteen percent more than windows without Low E coating. However, it's estimated that they reduce energy loss by as much as thirty to fifty percent.

[edit] Disadvantages

Low E coatings can reduce a window's visible transmittance, discoloring the window slightly and blocking some of the visibility. A spectrally selective Low E coating does not block visibility.

[edit] Suggested Application

Industry experts suggest that homeowners apply a Low-E coating to the outside pane of glass on a double or triple pane window which is located in a warm climate. This is particularly true for homes which are located in hot climates, for south-facing unshaded windows and for east and west-facing windows.

For homes located in a cold climate where the windows are designed to prevent heat transfer in the winter in order to maintain the heat inside of the house, the Low E coating should be coated on the inside pane of glass. Low E coatings may be applied in either hard or soft coats.

[edit] Soft Low E Coating

Soft Low-E coatings degrade when they are exposed to air or moisture. They can damage easily and are effective for a limited amount of time. For this reason window manufacturers use them on the inside of an insulated multiple-pane windows.

[edit] Hard Low E Coating

Hard Low-E coatings are a more durable coating. They are generally used for replacement window applications. However, the energy performance of hard Low E coatings is not as effective as that of soft coat coatings.

[edit] Self Application

In general a Low-E coating is usually applied during the window's manufacturing process. However there are do-it-yourself Low-E films. These coatings can last ten to fifteen years without peeling, increase thermal insulation and save energy. They are generally less costly than the inclusion of a Low E film which is coated on a window in the factory.

[edit] Types of Low E Window Coatings

Each type of Low E coating has been designed to allow for a different level of solar gain. There are high solar gain Low E coatings, moderate solar gain Low E coatings and low solar gain Low E coatings.

[edit] High Solar Gain Low E Glass

High-solar-gain low-E glass is most frequently manufactured using pyrolytic low-E coatings or sputtered high-solar-gain low-E film. Windows which are coated with a Low E film for high-solar-gain are generally installed in homes which are located in heat-dominated climates. They are often used in conjunction with passive solar design projects. High solar-gain glazings perform best in the winter where the priority is to lower solar gains.

[edit] Moderate Solar Gain Low E Glass

Moderate solar gain Low E windows are also referred to as windows with spectrally selective low-E glass. They reduce solar heat gain as they retain high visible transmittance. The moderate solar gain Low E glass reduces heat loss and permits a reduced amount of solar gain to transfer into the home which makes these windows suitable for climates that have both heating and cooling concerns. Moderate-solar-gain low-E glass is often produced with sputtered low-E coatings though pyrolytic moderate-solar-gain low-E is also employed.

[edit] Low Solar Gain Low E Glass

The glazing of low solar gain Low E glass windows is often referred to as spectrally selective low-E glass due to its ability to reduce solar heat gain while retaining high visible transmittance. When compared to most reflective and tinted glazing this low solar gain low-E glass provides an increased level of visible light transmission as it reduces solar heat. New low-solar-gain low-E coating variations have reached the market as well -- they are slightly tinted. Low solar gain Low E glass reduces heat loss in winter and reduces solar heat gain substantially in both the summer and the winter. Low solar gain Low-E glazings are appropriate for homes located in cooling-dominated climates. Low solar-gain glazings perform best in the summer where the priority is to raise solar gains.

Low solar gain Low-E glass is generally manufactured using sputtered Low-E coatings which consist of either two or three layers of double silver or triple silver Low E film.

[edit] Window Styles

Low E coatings are used in conjunction with single pane, double pane and triple pane replacement window applications. In addition they are appropriate for all window styles including hinged casement, awning and hopper windows, vertical sliding double hung windows, horizontal sliding glider windows and windows of special architectural shapes.

[edit] Energy Savings

National Fenestration Rating Council (NFRC), the body that many governmental agencies rely on for accurate assessments of window performance, estimates that the inclusion of a Low E film can lower a window's U-Factor by close to 10% and its Solar Heat Gain Coefficient by close to 30%. When included in conjunction with multi-pane glazing the inclusion of a Low E film on a window can help reduce energy costs significantly -- one study, carried out in a cold climate, estimated that energy costs were reduced by between 21% - 26% due to the Low E coating which had been applied to the windows.

[edit] All Climate - All Season

This type of glass maximizes the temperature you set either by heating or air-conditioning (or both) in your home. It allows light in but insulates from excessive heat entering or heat escaping.

[edit] Solar Control

Solar Control glass is engineered for the maximum insulation from the sun’s rays and maintenance of cool air from air conditioning. It isn’t tinted at all at resembles normal glass.

[edit] Glare Control

This type of glass does have a small amount of tint. What it does is absorb the light from the sun, muting its sharp rays and only allowing a soft glow to permeate your home. The glass will be warmer to the touch than normal glass, but not to a dangerous degree.

[edit] Winter Climate Glass

Winter Climate Glass offers the best protection from cold air. It allows for the most penetration of warmth and sunlight while offering a seal that won’t let as much warmth from heat escape.

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