Industrial heaters are used to covert energy from a fuel or energy source to thermal energy in a system, process stream or closed environment. The process by which thermal energy is transformed from an energy source to a system can be described as heat transfer. 

Residential heater tanks typically are no larger than 100 gallons, while commercial tanks do not exceed 250 gallons. While residential heaters usually handle gas inputs up to 75,000 British thermal units (BTUs), commercial units intake 1 million BTUs.