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For homeowners, how comfortable a house feels can be just as important as its energy efficiency. An older win- dow with a lower glass temperature feels colder be- cause more heat is radiated from a person’s body to the window.

Cold glass can also create uncomfortable drafts as air next to the window is cooled and drops to the floor. This sets up an air movement pattern that feels drafty and accelerates heat loss.

High-performance windows with lower u-factors will result in a higher interior window temperature in winter and thus greater comfort. Proper installation along with weatherstripping designed to seal tightly will also improve comfort by reducing cold air leakage.

During the summer, direct sunlight strikes people and surfaces, creating overheating and discomfort. Windows with low solar heat gain coefficients will re- duce the solar radiation coming through the glass. Low solar heat gain low-e glass reduces heat gain while still providing sufficient light and view.

High-performance windows with new glazing technologies make homes more comfortable. They create warmer interior glass surfaces, reducing frost and condensation. High-performance windows with warm edge technology and insulating frames have such a warm interior surface that condensation on interior surfaces is significantly reduced under all conditions.

Another concern for homeowners is the effect of sunlight on the home and its contents. Many organic materials, such as carpet, fabrics, paper, artwork, paints, and wood may fade upon exposure to sunlight. Window selection can influence the type and intensity of transmitted radiation.

Ultraviolet (UV) rays are the most harmful radiation in sunlight. They are the most energetic and thus most likely to break chemical bonds, leading to fading and degradation.

Coatings on glass can reduce the UV transmitted by up to 75%. UV absorbers can be incorporated into thin plastic films in multilayer windows or as an interlayer in laminated glass. In both cases, the UV transmission can be reduced to less than 1%. However, it is important to note that the remaining visible light that is transmitted can still cause fading in some materials. Using low-e coated glass or windows incorporating plastic layers rather than clear uncoated glass will reduce fading.



> Air Infiltration
The amount of air that passes between a window sash and frame, measured in cubic feet per minute per square foot of frame area.

> Argon Gas
A colorless, odorless, inert gas that fills the otherwise empty space within an insulating glass unit.

> Efficient Windows Collaborative
Organization that provides detailed reports and studies on the value of using high-performance windows. Visit the website at for more information on the studies cited in this article.

> Insulating Glass (IG)
Glass units constructed of two or more glass panes separated by a hermetically sealed space.

> Low Emissivity Coating (low-e)
Low-e coatings reduce energy transfer through insulating glass units, and thereby achieve one of the highest levels of energy performance possible for glass.

> Solar Heat Gain Coefficient (SHGC)
Measures the fraction of solar energy admitted and indicates how well the product blocks heat caused by sunlight.

> U-factor
Based on a window’s resistance to heat flow and its insulating value.

> Warm Edge Technology
The use of low- conductance spacers to reduce heat transfer near the edge of insulated glazing.

Equipped with durable extruded aluminum cladding, HP (low-e/argon) laminated glass with a PVB inner layer, this window stands strong during the harshest conditions and can even withstand the impact of wind-blown objects.

The 1125 series exceeds Energy Star requirements by 300%, says the manufacturer. These windows are a beautifully engineered combination of frame and glass that boasts up to R-11.1 insulation.

GreenBuilder 11.2010

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