The GT-540X3-PIH is well suited for residential applications. American has combined water heating and treatment in a product designed to revolutionize tankless water heating. Our new condensing gas tankless line features X3™ Scale Prevention Technology to last three times longer than other tankless models without X3™ Technology. Complies with Ultra-Low NOx regulations. The GT-540X3-PIH utilizes commercial grade copper alloy for the heat exchanger tubing. Certified up to 10,100 ft. altitude. ENERGY STAR® qualified X3™ Scale Prevention Technology 15-year limited Heat Exchanger Warranty, 5-year parts warranty, 1-year labor warranty for Residential applications Commercial Grade Copper Heat Exchanger Complies with Ultra-Low NOx regulations of less than 14 ng/J (<20ppm) Condensing Indoor model Safety features include freeze, overheat, surge protection, and troubleshooting diagnostic codes