Blower Door Test
A blower door test is the standard measurement of building airtightness. A calibrated fan mounted in an exterior doorway depressurizes (or pressurizes) the home to a known pressure — typically 50 Pascals — and the fan reports the CFM needed to maintain that pressure. From that single measurement, you can derive ACH50 and the home's natural infiltration rate. A blower door test is required for IECC code compliance, Energy Star certification, and Passive House certification.