RELIANCE WATER HEATERS ATHR-180M 1**

The registry does not publish the 178 therms figure. This site calculates it from the registry's UEF, the ratio of hot water delivered to energy used, and from the daily hot-water draw that the DOE test sets for the high draw pattern. This model's UEF is 0.95, from the DOE CCD, retrieved 2026-09-19. The result applies only to natural gas and only at that test draw. A household that uses more or less hot water each day than the test assumes will have a different yearly total. This page does not have that household's own figure. The calculation steps are explained in how the annual water heater energy and cost figures are calculated.

The high draw pattern describes a larger household, or one where showers and laundry overlap. In that group, this unit has the 45th lowest energy use of the 397 registered gas tankless models. That puts it in the lowest quarter of its class for energy use. The registry also lists a maximum flow rate in gallons per minute of 5.3 for this model. Whether 5.3 covers the fixtures a given home runs at the same time depends on that home, and this page does not have that information. No energy figure for a smaller draw pattern is available here. So a home with lighter daily use falls outside the figure shown. To compare another model in the same class, use the same-class replacement lookup by model number.

The running cost is not stated in this text because it depends on your own gas rate. The page calculates it from the ZIP you enter. It applies that state's average residential natural gas price to 178 therms, so the result changes from one state to another. The same applies to the 4 therms gap from the class median. What that gap costs over a year depends on the local gas price and is not stated here. To see the cost at your own address, use the running cost calculator for your ZIP. The installed price range has its own block on this page, with its source and date. It is a modeled range, not a quote.