Air flowing in and out of a building can cause lots of problems; in fact, air leakage can account for 30 percent to 50 percent of the heat loss in some homes. But air flowing through a building can help solve lots of problems too — as long as it’s the result of a blower-door test. With a blower door, builders can quantify airflow and the resulting heat (or cooling) loss, pinpoint specific leaks, and determine when a home needs additional mechanical ventilation.

First developed in the 1970s as a research tool, a typical blower door consists of a powerful variable-speed fan mounted in an adjustable panel temporarily set up in a doorway. The fan moves air through the building in a controlled fashion, while a pressure gauge — connected to the fan and to the outdoors by small-diameter pressure tubes —...

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