RINNAI (RX199I) REU-NB3237FF-US

This site computed the 173 therms figure; the registry does not publish an annual number. The inputs are the registry's UEF, the ratio of hot water delivered to energy used, and the DOE test's daily hot-water draw for the high draw pattern. For this model the UEF is 0.98, from DOE CCD data retrieved 2026-09-19. The result holds only at that test draw. A home that draws more hot water than the test assumes will use more gas than 173 therms. A home that draws less will use less. Among the 397 gas tankless models registered at the high draw pattern, this one ranks 1st lowest for energy use. The steps are set out in how the annual cost is calculated.

The high draw pattern stands for a larger household, or one where showers and laundry overlap. If that describes the home, 173 therms is the figure to check against. This model's maximum flow rate in gallons per minute is 5.8, as registered. That is the most hot water it delivers at once. The data here does not say how many fixtures that flow covers. A smaller household with lighter use is not what the high draw pattern tests, so neither the annual figure nor the rank describes it. Models tested at other draw patterns sit outside this class of 397, and no comparison with them is made here. For that wider comparison, use the water heater selector by fuel, space and size.

The running cost is not written in this text. It equals 173 therms multiplied by the reader's state average residential gas price, and that price differs by state. The page therefore computes it from your ZIP, and the cost calculator for your own ZIP runs the same calculation. The 9 therms gap to the class median, noted above, is priced at that same rate. The installed price range appears in its own block, with its source and date. It is a modeled installed-cost range, not a quote. If you are matching a unit already in place, you can find a same-class replacement by model number using (RX199I) REU-NB3237FF-US.