ACCORDING TO ADVANCED Energy, a nonprofit corporation based in Raleigh, N.C., about 20 percent of a house's heating and cooling costs are caused by heat gained or lost through the windows. A leaky window that lets in cold air during winter and warm air during summer is one of the biggest sources of energy inefficiency.

But windows have come a long way since the old days, and they just keep getting better. Additionally, more jurisdictions are passing tougher codes that require builders to use products with higher energy ratings. “Recent events such as the rise in energy costs and the active 2005 hurricane season will likely place greater attention and emphasis on the performance of windows and doors,” says Mark Mikkelson, manager of code, regulatory, and technical marketing at Bayport, Minn.–based Andersen Windows.

For example, New York state recently adopted codes requiring that windows be thermally efficient as well as impact resistant. And New Jersey has adopted the International Building Code's strict standards for wind resistance and structural loads. Expect this trend to continue, as more jurisdictions adopt ever-more-stringent energy and impact-resistant building codes to deal with higher fuel costs and unpredictable weather patterns.