There are more than 100 million homes and approximately 20 billion square feet of clear-glass residential windows in the U.S. Most of those homes are more than 30 years old, and as a result, the market is growing for replacement windows with energy-efficient insulating glass. High-performance options are now readily available in all regions of the country. Windows with U-factors and solar heat-gain coefficients less than 0.3 are now standard. And the cost of upgrading from conventional double-pane windows to double-pane low-E units with argon gas is less than $1 per square foot. Heating and cooling energy savings of 10 percent to 20 percent or more are possible, depending on the climate region and the replacement-window choice. Similar savings can be achieved in new construction by upgrading to high-performance glazing. Compared with clear glass, almost all of these new products reduce ultraviolet (UV) radiation and cut fading damage due to UV by 50 percent or more.

Since there are hundreds of window manufacturers, each with many different product offerings, it's easy to get confused trying to sort through the trade names and marketing hype. Window options used to be limited to single-pane versus double-pane and wood frame versus aluminum frame. Today, there are three or four basic frame types, double- and...

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