Here's a look at how the audit at Paul and Maddy's home took inventory of potential trouble spots.

Exterior Walls
Even when a house has been insulated, the materials' thermal effectiveness can be diminished by settling, wetness, or spotty installation. So the first place Torrey looks during an energy audit is inside the walls, to see where insulation is missing or has become compromised over time. To do this, he sets up a "blower door" test, creating an artificial windy day. He closes all the windows and doors, inside and out, then covers one exterior door opening with a thick plastic sheet that has a large fan embedded in it. By blowing air out the door, the fan lowers the air pressure inside the house. Gaps reveal themselves as fresh air begins to seep in to fill the vacuum. A pressure gauge measures how much air moves inside. (Similarly, Torrey uses a "duct blaster" on forced-air systems to check for ductwork leaks.)

With the blower door running, Torrey can scan the entire house with a camcorder-size infrared camera, which produces an image that registers temperature differences inside walls, attics, ceilings—anywhere leaks occur. Though an energy audit will work in any weather, the best time to do one is during hot or cold extremes so that there is a distinct temperature difference between inside and outside. In the winter, anywhere cold air is coming in appears black on the infrared image. In the summer, hot air moving through walls looks white. By keeping an eye on these spots, he can pinpoint where insulation has failed or is missing.

One way to make up for missing insulation is to blow loose cellulose into small holes drilled in the walls and behind the siding. However, walking through this house on a hot summer day, Torrey confirmed what Tom suspected: A previous owner had already retrofitted blown-in fiberglass, but there were gaps in the protection at the top and bottom of the spaces between the studs. Together the pair identified trouble spots, then Tom marked the walls so he could come back and replace the fiberglass with slow-expanding urethane foam, which seals crevices and joints so breezes can't slip through. The product (Icynene and Demilec are two brands) costs more than fiberglass, but "you'll get a tighter job," says Tom. "You could cut your energy loss by half."
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