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New glazing technology has done wonders to improve the performance and energy efficiency of glass windows. To determine how effective a particular window is, simply check its energy-efficiency rating.
measures a material's resistance to heat transfer; the higher the R-value, the better the insulation.
evaluates overall energy efficiency by measuring heat loss through the entire window, including the frame.
If you live in a cold climate, a high R-value and low U-value will likely be worth the investment.
A window's energy efficiency is determined by three factors: the glazing layers, material, and coating.
The more layers, the more effective the insulation. Single, clear glazing provides the least protection from the elements, with a rating of R-1. A double pane window can cut heat loss in half, or by even more if the air space between panes is filled with a low-conductance gas such as Argon. Triple, clear glazing introduces a middle layer of glass or plastic film.
Clear glass is the classic glazing material, but tinted glazing is a more effective barrier to solar glare and heat. Heat-absorbing glass contains a special tint that absorbs nearly 50% of incoming solar energy.
Reflective and Low-Emissivity (Low-E) coatings improve window performance in both the heating and cooling seasons. Reflective film reduces light and prevents heat gain. Low-E glass allows full light, but reduces heat transfer considerably. Low-Emissivity glass transmits 40% to 70% less heat than clear, untreated glass.
Combinations of these features produce a wide array of efficiency grades to suit every climate and budget.
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