Apparatus and methods for detecting leaks in a heat exchangers use mass gas flow metering. A regulated gas supply passes through a mass flow meter before entering either the product chamber or media chamber of a heat exchanger. The regulated gas supply passes into the heat exchanger through an inlet connection. All other inlets and outlets to the testing chamber are closed and isolated so that the chamber holds an applied pressure. The chamber on the opposite side of the heat exchanger is opened to atmosphere. Once gas fills the chamber and a static pressure is realized, the test begins by simply monitoring gas flow. If no flow is indicated, no flow rate is detected, and there is no detectable leak. Gas flow into the test chamber, at any given flow rate, as sensed by the sensitive mass flow meter, is an indication that leakage between the chambers exists.