Blower Door Test

A technician seals a calibrated, variable-speed fan into an open exterior doorway with an adjustable panel, then runs the fan to either pull air out of the house or push it in. This is how a blower door test measures how much air leaks through a home's envelope. That fan action creates a pressure difference between inside and outside, usually 50 pascals, and the equipment reads how hard the fan must work to hold that pressure. A leaky house needs a lot of airflow; a tight house needs very little.

The result is reported as air changes per hour at 50 pascals, written ACH50: how many times the home's full volume of air leaks out in an hour under that test pressure. Lower is tighter. The International Energy Conservation Code (IECC) requires a blower door test on new homes and sets a maximum, commonly 3 to 5 ACH50 depending on the code edition and climate zone the local jurisdiction has adopted. The test also helps a technician find the actual leaks, often with a smoke pencil or infrared camera while the fan runs.

For example, on a new Gilbert custom home, the rater runs the blower door near the end of construction. If the house tests at 6 ACH50 and the adopted code caps it at 5, the builder seals top plates, can-light penetrations, and rim joists, then retests until it passes. In Arizona's heat, a tighter envelope means the air conditioner moves less hot outdoor air and runs less.

A blower door test measures air leakage, not insulation value. Insulation is rated by R-value and slows heat conduction; air sealing stops air movement. A home can have great insulation and still fail the blower door if it leaks. Both are needed, and the test is how the air-tightness half gets verified.