ProLine XE Ultra-Low NOx Indoor Natural Gas Tankless Water Heater with X3 Technology - 240HX3. Highly efficient condensing hot water heater delivers up to .94 Uniform Energy Factor (UEF). Maintains like-new performance for the life of the product vs. tankless models without X3 that show 10% efficiency reduction in the first 1.5 years Primary commercial-grade copper heat exchanger is 25x better than stainless steel at heat transfer, stabilizing outgoing water temperatures quicker. Secondary heat exchanger is made of 316L Stainless Steel to protect against corrosion. Safety features include exhaust & water temperature safety control, overheat cut-off fuse and air-fuel ratio (AFR) sensor. Wall-mount design saves valuable space and allows for additional storage and flexibility. Industry leading “Peace of Mind” 15-year limited warranty covers scale-related failures. The ProLine XE Condensing Ultra-Low NOx Indoor Tankless Water Heater with X3 Scale Prevention Technology delivers continuous hot water, while protecting against scale build-up. Scale is the #1 enemy for tankless technology. With normal use, typical gas tankless water heaters begin to scale up over time. Scale reduces efficiency and increases annual cost of operation. Regular descaling is required to keep typical gas tankless water heaters operational, leading to ongoing maintenance costs. An expert in both water heating and treatment, A. O. Smith has combined the two technologies to achieve unparalleled protection on our condensing gas tankless water heaters with X3 Scale Prevention Technology. The technology prevents scale buildup, meaning virtually zero lifetime descaling maintenance and up to $2,800 in maintenance cost savings over the life of the product. X3 Scale Prevention Technology provides protection for the heat exchanger—making it last three times longer than a standard tankless water heater and maintaining like-new performance. A. O. Smith stands behind this revolutionary product with the industry’s first ever “Peace of Mind” limited warranty. Unlike competitive warranties, this 15-year limited warranty covers scale-related failures should they occur. The ATI-240HX3-N tankless water heater uses up to 160,000 BTU/hr of natural gas to deliver an endless supply of hot water for a 2 bath home in northern climates and up to a 3 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 0.94, and complies with Ultra-Low NOx regulations. With an industry leading 15-year limited warranty, the ATI-240HX3-N tankless water heater provides years of hot water through innovation and quality. These tankless water heaters utilize commercial grade copper alloy for the heat exchanger tubing and are approved to work with an external recirculation pump and cross-over valve. Certified up to 10,100 ft. altitude. 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.