The Lochinvar Copper-Fin 2 100138401 Natural Gas Commercial Pool Heater 990K BTU is a pool heater that offers a remarkably high thermal efficiency, dramatically reducing the operating cost of the equipment. It achieves this efficiency through the combination of an advanced fan assisted combustion system and a gasketless heat exchanger. The heat energy from the combustion process is transferred to the water as it passes through the copper finned tube heat exchanger. Additionally, the sealed combustion design of the unit eliminates external heat losses, which means energy heats the water directly, rather than being wasted on the surrounding mechanical room or poolside enclosure.