Monitoring method and system are provided for dynamically determining flow rate of a first fluid and a second fluid through a heat exchanger. The method includes: pre-characterizing the heat exchanger to generate pre-characterized correlation data correlating effectiveness of the heat exchanger to various flow rates of the first and second fluids through the heat exchanger; sensing inlet and outlet temperatures of the first and second fluids through the heat exchanger, when operational; automatically determining flow rates of the first and second fluids through the heat exchanger using the sensed inlet and outlet temperatures of the first and second fluids and the pre-characterized correlation data; and outputting the determined flow rates of the first and second fluids. The automatically determining employs the determined effectiveness of the heat exchanger in interpolating from the pre-characterized correlation data the flow rates of the first and second fluids.