blowerdoor

A blower door is a diagnostic tool used to assess the airtightness of a building. It involves a calibrated fan mounted in an exterior doorway that creates a controlled pressure difference between the inside and outside of the structure, allowing measurement of unintended air leakage through the building envelope.

To perform the test, the interior is prepared by sealing exterior openings and ensuring HVAC systems are off. The blower door unit is installed in a door frame and used to depressurize or pressurize the building to a standard pressure difference, typically 50 Pa. A manometer or differential pressure sensor records the pressure while the fan flow is measured. The test yields the airflow at 50 Pa (Q50) and, when combined with the building volume, a figure commonly expressed as air changes per hour at 50 Pa (ACH50). For a building volume V (in cubic meters), ACH50 = Q50 × 60 / V. Testing at additional pressures (for example 25 Pa and 75 Pa) can be used to derive a leakage coefficient and exponent in the relation q = C(ΔP)n, which characterizes how leakage changes with pressure.

Standards and applications: blower door tests are covered by standards such as ASTM E779, ISO 9972, and EN 13829. They are widely used in energy audits, building energy codes, certification programs, and retrofitting projects to guide improvements in energy efficiency and occupant comfort. They are often combined with diagnostic tools like duct leakage tests to identify specific leaks and prioritize sealing measures.

Limitations: results can be influenced by outdoor wind, temperature, and outdoor conditions; the test assumes HVAC systems are inactive and doors and windows are arranged as specified. It identifies total envelope leakage but does not localize leaks without complementary diagnostic methods.

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