A purge air control for a regenerative thermal oxidizer (RTO) having a plurality of exhaust towers containing a heat-exchange media includes a controller to determine an amount of clean air needed to purge the media. The controller opens a balancing damper to draw the determined amount of air into the RTO to purge the solvent-laden air from the heat-exchange media. As such, by determining the precise amount of air needed to purge the heat-exchange media, energy consumption associated with the purge process is reduced.