A. O. Smith is expanding its line of high efficiency residential gas tankless water heaters with the compact 120,000 Btu/hr. condensing tankless water heater. Measuring at less than two cubic ft. and scoring a .93 Energy Factor rating, this water heater efficiently utilizes energy and installs on the wall. Available in natural gas or propane, the Energy Star residential gas water heater is offered in two models: indoor, ATI-140H, and outdoor, ATO-140H. The unit operates on a 1/2” gas line, features accessible temperature controls and vents with PVC.