Available from 300,000-4.5 Million BTU/hr, the THP Series of direct-fired make-up air heaters use a combination of features (electronic modulating burner controls, remote thermostats, centrifugal blowers) to provide controlled, evenly distributed, warm, dry air. Centrifugal blowers provide large volumes of air at higher static pressures, allowing the equipment to work well with ductwork and helping to stimulate more air movement within the enclosed space. Use either propane or natural gas.