Diagnose problems in the building envelope with this simple, reliable tool.

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 ( see Figure 1, next page ). The fan moves air through the building in a controlled fashion, while a pressure gauge — connected to the fan and to the outdoors by smalldiameter pressure tubes — measures the rate of airflow required to maintain the building at a certain pressure. The blower creates exaggerated air leaks, which can then be found with the help of tools like smoke puffers or infrared cameras, or even just by feeling with the face or the back of the hand.

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