ProLine XE Concentric Vent Indoor 199,000 BTU Non-Condensing Natural Gas Tankless Water Heater with X3 Scale Prevention Technology - Indoor Natural Gas 510CX3 Continuous flow rate up to 10.0 GPM. Commercial-grade copper heat exchanger is 25x better than stainless steel at heat transfer, stabilizing outgoing water temperatures quicker. Easily convertible from natural gas to propane. Highly efficiency tankless water heater delivers up to .81 Uniform Energy Factor (UEF). Direct vent APNC35 concentric vent system, Vertical or Horizontal Vent Termination Installation. Includes integrated temperature controls and advanced diagnostics to simplify troubleshooting. Safety features include exhaust & water temperature safety control, overheat cut-off fuse and air-fuel ratio (AFR) sensor. 15-year limited warranty on heat exchanger in residential applications. Fully modulating, gas fired, tankless water heater with sealed combustion and power vented flue. Supplies hot water to domestic hot water systems (directly or indirectly) and can be used with water storage tanks, re-circulation systems (with use of a crossover valve), and/or combined domestic and heating applications. The ATI-510CX3 tankless water heater uses up to 199,000 BTUs of Natural Gas or Liquid Propane to deliver a max flow rate of 10.0 GPM. It utilizes condensing technology to achieve a Uniform Energy Factor of 0.81. This model meets Ultra-Low NOx requirements, and has a 15-year limited warranty on the heat exchanger in residential applications. A. O. Smith’s ProLine water heaters are residential products built to commercial-grade standards and are only available for purchase through professional wholesalers and contractors. Now equipped with X3 Scale Prevention Technology, these non-condensing units offer extended service life of up to three times longer than traditional/unprotected models.