Abstract: An improved regenerative thermal oxidizer ("RTO") and improved method of operating same in order to provide a substantially steady-state flow of contaminant-laden air into the RTO. The RTO includes an automatically-operated balancing valve structure for minimizing pressure variations experienced at the inlet of the RTO. The balancing valve is connected to and provides a selectively closeable bypass path for air flow between the high pressure and low pressure sides of an exhaust fan. The balancing valve opens the bypass path whenever flush valves of the RTO are all closed. The RTO further includes a hydraulic control system for minimizing variations in the operation of the RTO due to varying ambient or seasonal temperature conditions to which the RTO may be subjected. The RTO additionally includes a gravity-actuated damper valve structure near the top of a vertically arranged exhaust stack.