How Blower-Door Tests Measure Airtightness

Blower doors are variable-speed fans that are installed into a tightly fitting shroud in an exterior door opening. With the rest of the building closed up tight and interior doors open, the fan can be used to depressurize (or pressurize) the building and evaluate its airtightness.

Building scientists did not fully understand until the late 1970s that 25%–40% of the total heat loss or gain in a conditioned building can be attributed to air leakage. Not coincidentally, that is the same time the blower-door test was invented, independently, by two groups of researchers—the “Princeton house doctors” in New Jersey and a team led by Harold Orr in Saskatchewan.