By Donella Meadows

–March 18, 1993–

On a sunny, windless March morning Marc Rosenbaum of Meriden NH brought his blower door to the home of his neighbors, Carol and Gordon Ashey. His purpose was to measure the air-tightness of the Ashey’s two-bedroom, single-story house, and to demonstrate the blower door to three interested onlookers — Mike Currier, an eighth grader from the Plainfield School, Stephen Beaupre, the school’s science teacher, and a local columnist.

It took Marc about five minutes to drape a bright red tarp over the sliding aluminum frame of the blower door, fasten the tarp with Velcro strips, expand the frame to fit into the open front door, and snap it into place. Suddenly the Asheys had a red tarp door with an elastic-lined round hole at the bottom, into which Marc set an enormous fan. “This is a serious fan,” he said. “If it were summertime, it would really keep you cool.”

At the tag end of winter the fan was not there to cool, but to increase the air flow through any cracks in the house, making them easier to find.

Rmmmmmmmmm. Marc turned the fan on, aimed outward. The tarp bowed in — the inside air pressure was lower than the outside. While Marc turned the fan up higher, he read off numbers from a dial for Mike to write down. The numbers measured the airflow through the fan at various pressure differentials. The leakier the house, the more air the fan has to move to maintain a given differential.

Marc typed the numbers into his laptop computer, which translated them into air leaks. If you add all the little leaks together, said the computer, they would equal 248 square inches of hole — the equivalent of an open window about 16 inches on a side. Marc entered the price the Asheys pay for heating oil, and the computer calculated the estimated cost of those leaks: $231 a year.

“Gosh!” said Carol Ashey.

“Let’s find out where the holes are,” said Marc Rosenbaum.

He turned on the fan again with the motor reversed, blowing in. The red tarp bent outward; the house had a positive air pressure. Marc pulled out a small bottle that generates puffs of smoke and held it near the kitchen door.

Gordon Ashey had put plastic over the door to seal it for winter, but the smoke rushed outward, not through the crack around the door, but at the edge of the casing where the door frame joins the wall. “I find lots of leaks in places like that,” said Marc. “People know enough to seal up their windows and doors. But they don’t think of the casings.”

Marc moved the bottle up to the ceiling light. The smoke wandered around aimlessly. “Pretty good,” he said. “There are often big leaks around recessed lights, but this one is OK.”

Under the sink the smoke streamed down the plumbing pipes into the basement. Around the kitchen walls it zoomed into switches and plugs. Wiring and plumbing can create some of the worst air leaks, because they make up-and-down channels connecting low holes and high ones — the perfect combination to draw in cold air at the bottom and let warm air out at the top.

As Marc moved from room to room, the smoke found cracks in windowsills and ceiling beams, closets, heating ducts, and the tops of basement walls. Mike followed behind Marc, marking each leak with a bright orange sticker. Later Gordon Ashey could follow the sticker trail with caulk and tape and stop up the places where heat and dollar bills were flying out of his home.

Marc told tales of leaks in other houses. Around sliding glass outside doors and even sliding pocket doors in interior walls. In the joints of wood-stove chimneys. Around bathroom vents, kitchen cabinets, and hatches to attics. Where masonry chimneys penetrate floor frames. “I almost lost my whole smoke bottle near one chimney, there was such suction to the outside.”

After studying houses in the Boston area, the Massachusetts Audubon Society concludes that air movements account for 20 to 50 percent of the heat loss from a typical house. A study in Florida calculates that if leaks in ductwork alone were repaired, the state’s winter peak electric load would go down by 5000 megawatts — the equivalent of five huge power plants.

It’s one thing to know theoretically that you can save fuel and money by making your house energy efficient; it’s another to watch smoke rush out the holes. It’s easy to resist spending a few hundred bucks to bring in a patching crew or do the patching yourself; it’s something else to know for sure that you can make that money back in one year of lower fuel bills — and then again every year thereafter. No one wastes energy on purpose. But together we waste enormous quantities because we can’t quite visualize how air seeps through cracks.

If you’d like more information on finding and fixing home air leaks, there’s a short, clear “Contractor’s Guide to Finding and Sealing Hidden Air Leaks,” available for $3.75 from the Public Information Office, Massachusetts Audubon Society, Lincoln MA 01773, telephone 617-259-9500.

Copyright Sustainability Institute 1993