ORBEK HS120

The registry does not print the 132 therms figure. This site computed it from two inputs. The first is the registry's UEF, the ratio of hot water delivered to energy used, which is 0.84 for the HS120. The second is the DOE test's daily hot-water draw for the medium draw pattern. Both inputs come from the DOE CCD, retrieved 2026-09-19. The result therefore holds only at the federal test's daily draw. It does not measure the gas use of any particular home. A plumber or seller comparing this figure with another source should check that both use the same draw pattern and the same UEF. The steps behind the calculation are set out on the page explaining how the annual cost is calculated.

Among the 80 models registered as a gas tankless unit at the medium draw pattern, the HS120 ranks 23rd lowest for energy use. Its 132 therms sits 3 therms below the class median of 135 therms. The comparison applies to households whose daily hot-water use is close to the medium pattern, which DOE describes as a typical household's busy morning. For a home that uses much more or much less hot water, the comparison does not carry over. The registry also lists a maximum flow rate in gallons per minute of 3. Peak demand above 3 gallons per minute is outside this rating. To compare other units by fuel, space and size, use the water heater selector.

The running cost of 132 therms of natural gas is not written in this text. It depends on the reader's state average residential gas price, so the page computes it from the reader's ZIP. Two homes with the same 132 therms can therefore pay different amounts in different states. To see the figure for your own rate, enter your ZIP in the cost calculator for your ZIP. The installed price range appears in its own block on this page, with its source and date. That range is a modeled installed cost, not a quote. If you are matching the HS120 to a unit in the same class, use the same-class replacement search by model number.