What does a blower door test measure?

A blower door test is a diagnostic tool used in building performance analysis to assess the air leakage characteristics of a building. It measures the amount of uncontrolled air that can infiltrate or exfiltrate through the building envelope by creating a significant pressure difference between the inside and the outside of the structure.

During the test, a fan is mounted in a doorway, and the air pressure inside the building is reduced or increased, depending on the test direction. By measuring the airflow through the fan while maintaining this pressure difference, the test can quantify how much air is leaking through cracks, gaps, and other unintentional openings in the building's envelope. This information is crucial for understanding how well-sealed a building is, which directly impacts its energy efficiency, comfort, and indoor air quality.

The other choices pertain to different aspects of building performance. Heat loss through insulation relates to thermal performance rather than air leakage alone. Ventilation effectiveness assesses how well fresh air circulates, which can be influenced by air leakage but is not measured directly by a blower door test. Humidity levels indoors focus on moisture control and comfort rather than airflow or pressure differentials.