Abstract: A system and method for determining “real time” air leakage from a duct involves an airflow meter for taking airflow measurements at the inlet and at the outlet of the duct. Also included is a base fan that operates in three different modes to simultaneously vary an enclosure pressure at the inlet and outlet. This is done while a duct fan, inside the duct, is operated to continuously move air through the duct. A comparison of airflow measurements at the inlet, or at the outlet, under the three base fan operational modes will respectively identify whether leaks are present in the duct, upstream or downstream from the duct fan.