GSW WATER HEATERS ATHR-180M 1**

The figure of 178 therms is computed by this site, not published by the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, which is 0.95 for this model, with the DOE test's daily hot-water draw for the high draw pattern. The fuel is natural gas, and the source is the DOE CCD, retrieved 2026-09-19. The figure applies only at that test draw. A household that uses more or less hot water than the federal test assumes will use a different amount of gas, and the data here gives no estimate for that case.

The model ranks 45th lowest energy use of 397, which places it in the lowest quarter of its class. The class median is 182 therms, and this model sits 4 therms below it. The comparison covers only the 397 models registered as a gas tankless unit at the high draw pattern. It says nothing about storage or electric models, so a reader weighing other fuels can use the water heater selector by fuel, space and size. The maximum flow rate in gallons per minute is 5.3 as registered. A first-hour rating is not available in the data used here, so this page does not state one.

The running cost is not written in this text because it depends on the state average residential gas price where the reader lives. The page computes it from the reader's ZIP, applied to 178 therms at the high draw pattern. The cost calculator on your own ZIP shows that result, and how the annual cost is calculated lists the inputs for anyone checking it. The 4 therms gap from the 182 therms class median changes the result only in proportion to that local price. The installed-cost range appears in its own block with its source and date. For a unit in the same class as this one, use the same-class replacement search by model number.