Monitoring method and system are provided for dynamically determining airflow rate through and heat removal rate of an air-conditioning unit, such as a computer room air-conditioning unit. The method includes: sensing inlet and outlet temperatures of fluid passing through a heat exchanger associated with the air-conditioning unit; sensing air temperature at an air inlet side of the heat exchanger; automatically determining at least one of airflow rate through or heat removal rate of the air-conditioning unit, the automatically determining employing the sensed inlet temperature and outlet temperature of fluid passing through the heat exchanger, and the sensed air temperature at the air inlet side of the heat exchanger; and outputting the determined airflow rate through or heat removal rate of the air-conditioning unit. In one embodiment, the heat exchanger is an auxiliary air-to-air heat exchanger, and in another embodiment, the heat exchanger is the air-to-liquid heat exchanger of the air-conditioner.