When you buy or replace a window or glazed door, you can choose from a variety of glazings. Usually, the more energy efficient the glazing, the more expensive it is. An R-value measures heat loss through glass. The way a window is glazed has much to do with its R-value: the higher the R-value, the more efficient the glass.

The U-value measures the amount of heat that can escape per hour through a given window. Two U-values are usually given: one for the glass and one for the entire window, including the frame. The lower the U-value, the more energy efficient the window.

Although single glazing a single sheet of glass was once the standard, dual glazing or insulating glass is now more common. This type of glass consists of two panes of glass separated by a thin air space and offers twice the R-value. You can also buy more effective triple glazing with dual air spaces.

There are several high-performance glazings on the market today. Low-E glazing is the most common. This uses an imperceptibly thin metallic film between two glass panes that selectively rejects some energy wavelengths, greatly reducing heat transfer and minimizing fading of furniture and carpets caused by ultraviolet rays. New super windows use two low-E films for ultra-high R-8 insulation values.

Argon gas-filled windows are even more energy efficient. When a window is injected with this natural, colorless, non-toxic gas, its insulating qualities are doubled.

-- Tips courtesy of HomeAdvisor.com