Tankless Water Heater Non-Condensing Ultra-Low NOx Outdoor 140,000 BTU Natural Gas

The 110U Series is great for apartments, one bath homes in cold climates, condos and summer cabins. The design allows for a variety of installation options. Complies with Ultra-Low NOx regulations and meets energy efficiency requirements of ASHRAE 90.1b-1992.

The ATO-110U tankless water heater uses up to 140,000 BTU/h of natural gas/liquid propane to deliver an endless supply of hot water for a 1.5 bath home in northern climates and up to a 2.5 bath home in southern climates (one shower head per bath). The ATO-110U is ENERGY STAR® qualified with a Uniform Energy Factor of 0.81. With an industry leading 15-year limited warranty, the ATO-110U tankless water heater provides years of hot water through innovation and quality.


  • Field Convertible From Natural Gas to Propane
  • Easily convertible from natural gas to propane with supplied kit.
  • Copper Heat Exchanger
  • 25x better heat transfer than stainless steel thus stabilizing outgoing water temperature quicker and reducing pressure drop across the heat exchanger.
  • Safety Features
  • Includes freeze, overheat, surge protection and troubleshooting diagnostic codes.
  • Space Savings
  • A. O. Smith tankless water heaters take up much less space that your conventional tank-style water heater. With no tank to steal valuable storage space, our wall-mount design allows for additional storage and flexibility.
  • Tech Specs
  • Emissions: Ultra-Low NOx
  • Maximum BTUs: 140,000
  • Minimum BTUs: 15,000
  • UEF: 0.81
  • Limited Heat Exchanger Warranty: 15 Years
  • Limited Parts Warranty: 5 Years
  • Water Connection Location: Bottom
  • Water Connection Size: 3/4"
  • Heat Exchanger: Copper
  • Voltage: 120
  • Remote Control: Yes
  • Technology: Non-Condensing
  • Dimensions & Venting
  • Type: Space Saving
  • Height: 20 1/2"
  • Width: 13 3/4"
  • Depth: 9 1/2"
  • Product Weight: 38lbs/17kg
  • Shipping Weight: 39