To improve energy performance of its projects, Byggmeister Associates, in Newton, Mass., conducts a blower-door test to determine airtightness. Crews previously used a smoke stick or would find the leaks by feel, but a year ago the company began using a theatrical fog machine to better indicate leaks. “When you’re testing a whole building envelope, it’s faster and more reliable to use the fog machine,” owner Paul Eldrenkamp says.


The company conducts the test after the insulation and air barrier have been installed, but before the walls are closed in with gypsum board. “That still gives you access to fix any leaks,” Eldrenkamp says.

To do the test, the crew pressurizes or depressurizes the house (for most diagnostic tests you depressurize), and places the fog machine inside or outside so they can “see” the air leaks.

At first, the remodeler rented a fog machine. “But we quickly realized that we used it enough to justify owning it,” Eldrenkamp says. The $500 machine requires a glycol-based solution, available in one-gallon containers. “We run it through the machine, then run distilled water through it to clean it out,” he says. The firm’s blower-door system cost $3,000.

Eldrenkamp says that most air leaks occur at changes in plane such as where floor joists meet a wall; at the eaves where a rafter connects to a sill plate; or at a knee wall on an upper floor. His crews have adopted practices to combat these typical leaks.

On a recent test, the crew saw a large amount of smoke blowing through a vent pipe. The cause: A plumber had forgotten to glue a pipe joint. Without the test, “we would not have found [the problem] until the joint started leaking after a rain,” Eldrenkamp says.

The test is especially useful for houses that have finished rooms over a garage. “For health, safety, and code purposes, we want to make sure there is a separation between those two spaces,” he says.


Eldrenkamp uses the Home Energy Rating System index to measure energy consumption (see “Measurable Goals,” right). He also tracks BTUs per square foot for projects, calculating this number by converting the total energy consumption for a house into BTUs and dividing that by the square footage. It provides a way to compare projects and changes. Eldrenkamp says, “We can tell a client, ‘You are at 65,000 BTUs per square foot per year, but our projects end up at less than 40,000.’ It’s useful in sales and goal-setting.”