A regenerative thermal oxidizer includes a heat exchange column formed of a body which defines at least one entire flow passage through the heat exchanger. The structure of the heat exchange column assists in purging residual gas to be cleaned from the heat exchanger prior to that regenerative heat exchanger moving into a mode where it receives the cleaned gas. The heat exchanger columns preferably have 70 to 80 percent of their surface area used as the flow passages. In a further geometric arrangement made possible by the inventive heat exchanger described above, two heat exchanger columns are positioned on opposed sides of a combustion chamber. End faces of the two opposed heat exchangers transfer radiative heat energy from the hotter of the two heat exchanger end faces to the cooler of the two heat exchanger end faces. In this way, radiative heat energy is not lost, but is reused to heat the other of the heat exchangers.