Last February, five window manufacturers and replacement contractors cut a deal with the Federal Trade Commission. The FTC had filed complaints against the five saying that their marketing made “exaggerated and unsupported” claims for energy savings.

In its action, the FTC cited claims that windows would save “40% [or] 50% on energy bills.” In its settlement, the FTC requires the companies to stop claiming “a specified amount or percentage of energy savings” unless the claims can be substantiated.

QUIETER & MORE COMFORTABLE Since energy savings are a key benefit of replacement windows, what legitimate claims can contractors make?

It's important to note that the potential energy savings from installing replacement windows varies from one climate zone to another and from house to house. “I never like to speak in absolutes,” says David Paulus, an engineer for Wasco Windows, a Wisconsin company that makes and installs replacement windows. Paulus says, based on testing of various windows under different conditions at Lawrence Berkeley National Laboratory, in California, that he will tell homeowners they can achieve “8% to 20% savings for all situations in a northern climate” under optimal conditions. Windows are about a quieter and more comfortable house first, with energy savings second.

GO TO THE SOURCE Christian Kohler, an engineer at Lawrence Berkeley Lab, says efficiency is based on approved U-factor and solar heat gain coefficient numbers. The lab tests windows of various types and for climate conditions in more than 50 cities in what it calls a “standard house” with 38 openings. (E.g., tests that show replacing a single-pane metal window in Chicago with a double-pane insulated vinyl window would result in a 21% savings.)

Kohler recommends that window replacement companies consult the selection tool on the Efficient Windows Collaborative site ( for recommendations based on specific climate zones; and the Energy Star site (