A regenerative thermal oxidizer (H-101) includes a number of heat exchange columns (A, B) topped by a combustion chamber (C-101). Contaminated air is directed into one of the columns and oxidation is completed as the flow passes through the combustion chamber (C-101). From the combustion chamber (C-101), the now clean air flows vertically downward through another column and then is directed via an outlet valve through an outlet manifold and released to atmosphere or recirculated back to the oxidizer (H-101). A combustible fuel is added to the contaminated air prior to its entry into one of the columns. The addition of the combustible fuel is regulated by continuously monitoring the inlet and outlet temperatures (TE-101A, TE-108A), and comparing a difference between these temperatures to a predetermined value. Further control can be achieved by measuring the flow of contaminated air to the oxidizer (H-101) via pressure differential and coordinating that measurement with the temperature differential measurement.