What is a blower door test and what is measured?

• A. A blower door test measures airtightness.
• B. A blower door test measures airtightness and identifies leaks.
• C. A blower door test measures the roof structure strength.
• D. A blower door test measures the rate of heat transfer through walls.

Answer: (D)

A blower door test measures airtightness by evaluating how much air leaks through the building envelope under a controlled pressure difference. A powerful fan is placed in an exterior door to pressurize or depressurize the space, and the airflow needed to hold a set pressure (often shown as ACH50) shows how leaky the building is. This test can also help pinpoint leak locations with smoke, infrared, or other inspection methods. It does not measure the roof structure’s strength, and it does not directly quantify the rate of heat transfer through walls; those aspects relate to insulation performance and are assessed by other tests or calculations.