The method of choice for measuring a home's tightness is a blower-door test. The most common techniques follow the ANSI/ASTM-779-99, "Standard Test Method for Determining Air Leakage Rate by Fan Pressurization" or the CAN/ CGSB 149.1 "Determination of the Airtightness of Building Envelopes by the Fan Depressurization Method." These standards follow similar test protocols and give very similar results.

A large fan is installed in one exterior door of the house, creating a pressure difference of 50 Pascal across all sides of the house at once-roughly equal to the pressure of a 25 mph wind. While a house would never experience this naturally, it enables simple and accurate leak detection. The fan is calibrated and the operator records the cubic feet per minute (CFM) that the fan is delivering at 50 Pascals of pressure. Often a range of pressures and airflows is recorded so that results can be reported in a variety of ways, including the three preferred metrics discussed below.