A.O. Smith continues to lead the way in residential and commercial water heating with close to 70 years of innovative hot water solutions. The ATO-540P-P is A.O. Smith's high efficiency, Ultra-Low NOx outdoor model, it keeps emissions low by featuring the latest in water heating technology. Switching on when a hot water tap is opened, a built in temperature sensor helps to maintain hot water within a one degree set point during use, and the system automatically shuts off when the tap is closed saving you energy. An on board controller gives you simple and complete control over your water heater. Integrated Recirculation Pump The ATO-P tankless water heater comes with a built-in integrated recirculation pump. A recirculation pump is designed to provide hot water to the home High Efficiency Condensing Technology The ATO-540P-P features the latest in water heating condensing technology. This means that the unit can deliver some of the highest efficiency standards on the market, keeping dollars in your pocket. Ultra Low-NOx Emissions The ATO-540P-P is designed to qualify for the most stringent Low-NOx standards. These standards coincide with SCAQMD rules and other air quality management districts. Heavy Duty Heat Exchanger The primary heat exchanger is built out of copper, offering better heat transfer than stainless steel and designed to be more resilient against corrosion. A.O. Smith water heaters are built to last and save you money in the process. Multiple Safety Features ATO models come with a long list of safety features standard. These include: built in freeze protection, manual reset hi limit, an overheat cutoff fuse, inlet and outlet thermistors to monitor temperatures, and a built-in flame sensor. Space Saving Design A.O. Smith tankless heaters take up less space than their conventional counterparts. The convenient wall mount design means they can fit in nearly any outdoor wall layout and offer additional flexibility.