How does a blower door test measure air leakage in a building?

A blower door test effectively measures air leakage in a building by using a fan to depressurize the space. This process involves attaching a calibrated fan to an exterior door frame, which creates a pressure difference between the inside and outside of the building. As the fan removes air from the interior, the building becomes depressurized, causing outside air to flow in through any existing leaks, cracks, or openings in the building envelope.

This inflow of air is then quantified, allowing for an assessment of how much air is escaping or entering the building due to leakage. The measurable airflow rates during the test help identify areas of concern where improvements can be made for energy efficiency, comfort, and indoor air quality. This method is much more reliable and precise than other approaches like visual inspections or measuring temperature or humidity levels. These other methods, while valuable, do not provide the direct measurement of air movement that the blower door test does.