This 4.9 GPM 150,000 BTU Natural Gas Tankless Water Heater has an automatic shutoff and operates only when needed to help you save on utility bills. It features dual stainless-steel heat exchangers and a 3-phase, pre-mixed burner to provide hot water reliably when needed. A built-in leak detector is included to provide peace of mind and help minimize energy loss. This efficient heater is Energy Star qualified for year-round savings. Also includes Circulation Pump with Mini Buffer Tank minimizing hot/cold/hot stacking, the so called Cold Water Sandwich.