Abstract: A process and apparatus used for heating and drying a material. The process uses supplemental radiant heat supplied by circulating thermal oil that is heated using fuels, as well as exhaust heat from other sources. The supplemental heat replaces a portion of the heat provided by the direct-firing. The supplemental heating is achieved by retrofitting existing direct-fired or radiant heat gypsum dryers with thermal oil-to-air heat exchangers in the combustion air lines and the air recirculation lines. Heated thermal oil is circulated through the exchangers, providing supplemental heat to both the combustion air and the re-circulated dryer air. The existing natural gas burners are fired to achieve the desired exit temperature. A Organic Rankine Cycle (ORC) system is coupled to the dryer exhaust vent to recapture heat energy produced by the thermal oil and produce electricity.