A method for determining the flow of an anode gas out of an anode sub-system. The method includes providing pressure measurements at predetermined sample times over a predetermined sample period and using the pressure measurements to calculate a slope of a line defining a change of the pressure from the beginning of the time period to the end of the time period. The slope of the pressure line is then used in a flow equation to determine the amount of gas that flows out of the anode sub-system, which can be through a valve or by system leaks.