Abstract: An air-permeable reactor medium of large surface area and high thermal capacity, coated with a catalyst, is cycled along a closed path across a first duct carrying an air stream laden with oxidizable contaminants and a second duct carrying a stream of fresh air, enabling contaminants in the first air stream to be oxidized to innoucuous byproducts, releasing heat which is transferred to the fresh air in the second duct, the reaction medium moving at a variable speed which is a function of the temperature of one of the air streams; considerable improvement in the efficiency of an industrial oven may therefore be achieved by positioning the reactor medium to exchange heat between an incoming stream of fresh air and a stream of hotter exhaust gas so that the temperature of fresh air delivered elsewhere to the oven may be controlled without having to rely on dampers and mixtures of air volumes with inherent damper malfunctions or mis-metering; also a second burner may be eliminated because of the manner in which t