an oxidation assembly catalytically oxidizes organic hydrocarbon gases and recovers the heat held by the heated oxidized exhaust generated by such oxidation . the assembly includes a preheater and a catalytic recuperative heat generator which contains a suitable oxidation catalyst . an outside air inlet provides communication between the outside air and the heat generator . the assembly also includes a fan having a first and second outlet for moving the heated oxidized exhaust , and an outside air preheat exchanger . the first outlet of the fan and a recirculation duct communicate to form a loop for storing the heated oxidized exhaust for later use , and the second outlet of the fan and the inlet of the catalytic preheater communicate to form a loop for returning the oxidized exhaust to the preheater . although the assembly may be designed with a fixed pre - adjusted gas flow control device , in the preferred embodiment , variable flow control devices are provided at various positions within the apparatus .