Thermal oxidizers, or thermal incinerators, are combustion devices that control VOC, CO, and volatile HAP emissions by combusting them to carbon dioxide (CO2) and water. Thermal oxidizers are similar to catalytic oxidizers (catalytic oxidizers use a catalyst to promote the oxidation reaction). Important design factors include temperature (a temperature high enough to ignite the organic constituents in the waste stream), residence time (sufficient time for the combustion reaction to occur), and turbulence or mixing of the combustion air with the waste gas.

To reduce fuel usage required for oxidation, thermal oxidizers frequently have some form of heat recovery. The percentage of heat recovery in the design of thermal oxidizers generally increases with decreasing inlet VOC/HAP concentration. Heat recovery may either be recuperative or regenerative. In recuperative heat recovery, heat is recovered by passing the hot exhaust gases through a non-contact air-to-air heat exchanger, to heat the incoming air to the oxidizer. In regenerative heat recovery, hot exhaust gases and cool inlet gases are alternatively passed through a fixed bed, typically employing ceramics.