RINNAI (RX180I) REU-NB2934FF-US

This site computed the 173 therms figure; the registry does not publish it. The figure 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 pattern. This model's UEF is 0.98. The class is the 397 models registered as a gas tankless unit at the high draw pattern. Within that class, this model ranks 1st lowest in energy use of 397. That rank puts it in the lowest quarter of its class. The figure applies only at the test's daily draw, so a home that uses more or less hot water will have a different yearly total. The source is DOE CCD, retrieved 2026-09-19. The steps behind the figure 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 173 therms figure describes that kind of home and no other. For this model, the registry lists a maximum flow rate in gallons per minute of 5.3. Hot-water demand above 5.3 at one time is beyond that rated flow. A smaller household that draws less hot water falls outside the test condition as well. This data gives no yearly energy figure for such a home, so that value is not available here. The registry data does not show how the unit performs at other draws. To compare other units by fuel, space and size, use the water heater selector.

This text states no running cost. The cost depends on your state's average residential gas price, so the page computes it from your ZIP code. Your rate is not available to this text, and no amount is estimated here. The yearly cost comes from multiplying 173 therms by that rate, at the high draw pattern only. At any given rate, the gap of 9 therms below the class median of 182 therms moves the cost in the same direction. The installed price block on this page shows a modeled range with its own source and date. That range is not a quote. To run the figure for a different address, use the cost calculator for your own ZIP.