The ATO-540HX3-N tankless water heater uses up to 199,000 BTU/hr of natural gas to deliver an endless supply of hot water for a 3 bath home in northern climates and up to a 4 bath home in southern climates (one shower head per bath). Our new condensing gas tankless line features X3™ Scale Prevention Technology to last three times longer than other tankless models without X3 Technology. This heater is extremely efficient with a Uniform Energy Factor of 0.93, and complies with Ultra-Low NOx regulations.. With an industry leading 15-year limited warranty, the ATO-540HX3-N tankless water heater provides years of hot water through innovation and quality.