For the last three years, A.O. Smith has been working with the U.S. Department of Energy (DOE) and the technology development firm TIAX LLC to increase efficiency in residential water heaters. This strategic partnership has resulted in the development of the A.O. Smith Vertex-a residential gas water heater that combines higher gas input and more-efficient combustion to deliver more hot water while reducing operating costs. Vertex features a glass-lined helical coil heat exchanger made from low-carbon steel, 90% thermal efficiency, 76,000 Btu/hr input rate and first hour rating of 127 gph. A.O. Smith. Circle 7.