An exhaust fan flow test measures the volume of air a ventilation fan removes from a home or building over a given period of time. Using a specialized flow meter, the test determines the fan’s actual airflow under installed conditions. The airflow rating listed on a fan’s label does not always reflect its real-world performance, as ductwork, installation, and other factors can affect how much air the fan actually moves. Proper exhaust airflow helps remove moisture, odors, and indoor air pollutants, supporting good indoor air quality and helping manage excess humidity. The results provide a measurable assessment of ventilation performance and help identify fans that may not be delivering their intended airflow.