The GTS-540X3 series is well suited for residential applications. State Water Heaters have 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 GTS-540X3 utilizes commercial grade copper alloy for the heat exchanger tubing. Certified up to 10,100 ft. altitude.