STATE ATHR-199M 1**

The 178 therms figure comes from this site's own calculation. It is not taken directly from the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, with the DOE test's daily hot-water draw for the high draw pattern. For this model the UEF is 0.95, as listed in the DOE CCD, retrieved 2026-09-19. The figure holds only at that test draw. A household that uses more or less hot water than the test assumes will have a different yearly total. That adjusted total is not available here. The steps behind the number are set out on the page about how the annual cost is calculated.

The high draw pattern describes a larger household, or one where showers and laundry overlap. The 178 therms figure applies to homes like that. It does not describe a smaller household on a lighter draw pattern. A figure for this model at other draw patterns is not available here. Flow sets a second limit. This unit is listed with a maximum flow rate in gallons per minute of 5.9. How many fixtures that covers at the same time depends on the home's fixtures and incoming water temperature. This page does not have that information. To compare units by fuel, space and size, use the water heater selector.

The class comparison in the summary above covers the 397 models registered as a gas tankless unit at the high draw pattern. The 4 therms gap to the 182 therms median puts this model in the lowest quarter of its class for energy use. That gap is measured at the test draw in energy units, not in money. The running cost is not stated in this text, because it depends on your state's average residential gas price. The page works it out from your ZIP in the cost calculator for your own ZIP. The installed-cost range shown in its own block on this page is a modeled range with its own source and date. It is not a quote.