Credit: Tim Healey

You can't gauge the truth of an opinion by the frequency of its repetition. Exhibit A: Builders' opinions concerning energy, insulation, heating, and cooling. A fair percentage of these beliefs — derived in part from product marketing, obsolete recommendations from "experts," and oft-repeated tales heard at lumberyards — prove upon examination to be half-truths or outright misconceptions. But like Whac-a-Mole pests, they just keep popping up. To set the record straight, this article will strive to clobber the pesky moles one more time.

"Window replacement is a cost-effective way to save energy."

Replacing old single-pane windows with new double-pane low-e units certainly saves energy. But the cost is so high — and the amount of energy saved is so low — that window replacement is almost never cost-effective. Depending on the climate and the window cost, the payback period for replacement windows can be as long as 20 or 30 years.

According to calculations posted on an Energy Star program Web site, installing new double-pane low-e windows in a typical 2,000-square-foot single-story house that previously had single-pane units will result in annual energy savings of $125 (in a mild climate like California's) to $340 (in a severe climate like New England's). If the old windows had storms, the savings drop to $20 to $70 per year. Exact mileage may vary, but anyone who expects that window replacement will have an energy payback needs to be prepared for a very long wait.

The most cost-effective window retrofit measure is the installation of low-e storm windows. Although many storm-window suppliers are unfamiliar with the product, low-e storms can be ordered. Suitable glass with a pyrolitic (hard-coat) low-e coating is available from most glass distributors. According to a recent study, the payback period for installing low-e storm windows on older houses in Chicago averaged just 4.3 years.