- ENERGY STAR® certified
- 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
- Highly efficient condensing Ultra-Low Nox tankless water heater delivers up to .95 Uniform Energy Factor (UEF)
- Recirculation pump capable with the use of a cross-over valve. Sold separately.
- Ideal choice for residential single-family applications with continuous hot water needs and hard water concerns
- Safety features include exhaust & water temperature safety control, overheat cut-off fuse and air-fuel ratio (AFR) sensor
- Industry leading “Peace of Mind” 15-year limited warranty covers scale-related failures
The ProLine® XE Condensing Ultra-Low NOx Outdoor 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 ATO-540HX3-P tankless water heater uses up to 199,000 BTU/hr of Liquid Propane to deliver a continuous 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). This ENERGY STAR® certified tankless water heater is extremely efficient with a Uniform Energy Factor of 0.93, and complies with Ultra-Low NOx regulations. 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 standard and are only available for purchase through professional wholesalers and contractors.