The more energy efficient a home, the more it usually costs to build. Utilities market their energy-efficient building programs by promising customers that lower heating and cooling bills will more than offset any extra cost. A Home Energy Rating Systems, or HERS, is one way to quantify those claims. The idea is similar to the energy ratings used for windows (see "NFRC Simplifies Window Ratings"). The ratings can also be used to qualify homes for energy-efficient mortgages. But while a number of HERS programs have cropped up around the country, the lack of a national standard has stunted their growth.

Help has arrived. In accordance with the Energy Policy Act of 1992, the Department of Energy just published a set of voluntary HERS guidelines, and is encouraging utilities and the mortgage industry to adopt them. The new guidelines would assign each home a rating of between 0 and 100, based on how well it conforms to insulation requirements of the Council of American Building Officials' Model Energy Code, as well as air leakage and other requirements listed in the HERS guidelines. According to Dick Tracey, a Washington-area consultant who co-chaired the HERS Council technical committee, some of these other requirements are stricter than the MEC. A home that uses as much energy as the MEC home gets 80 points. The house gets an extra point for every 5 percent in energy use reduction, and loses a point for each 5 percent rise in energy use. The rare home that needs no purchased energy would get a perfect 100. That would require a home with 100 percent solar heating (no backup) and complete photovoltaic electricity system.