500K BTU indirect fired heater operates like a mobile furnace with a fan forcing air over the heat exchanger where internal combustion occurs and fumes are exhausted through a stack. 100% Clean dry heat with no open flame. Great for special events where ducting allows for the unit to be placed outside and away from the tents or structures with warm air ducted into interior areas. Can be ducted up to 100' away from heater. Diesel Fuel sold separately.