The 540 series integrates a recirculation pump to provide instant hot water in residential applications with dedicated recirculation lines. The pump is easily controlled with a simple user interface and multiple pump settings allow you to customize pump operation to meet your needs while maximizing heater efficiency. The onboard computer modulates combustion to yield an Energy Factor of 0.95 while meeting the strictest gas emissions standards. As part of the high efficiency tankless family, the 540 series provides endless hot water while being environmentally friendly. The GTS-540-NIH 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). Utilizing condensing technology, this heater is extremely efficient with an Energy Factor rating of 0.95 and is ENERGY STAR® qualified. With an industry leading 15-year limited warranty, the GTS-540-NIH tankless water heater provides years of hot water through innovation and quality.