A variable volumetric flow heat exchanger for a building air-to-air heat recovery system that is operable at a high volumetric flow rate and at a low volumetric flow rate. The heat exchanger includes multiple heat exchange banks, including at least one continuous duty heat exchange bank, and at least one cyclic heat exchange bank. A damper assembly includes at least one damper module having at least one damper reciprocative between open and closed positions. A control system moves the heat exchanger damper to the closed position when the heat recovery system is operated at the low volumetric flow rate and moves the heat exchanger damper to the open position when the heat recovery system is operated at the high volumetric flow rate.