ENVO WH-AZ51-180-NGO

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.82 for the ENVO WH-AZ51-180-NGO. The annual figure is not a registry value. This site computed 206 therms of natural gas from that UEF and the DOE test's daily hot-water draw for the high draw pattern, using DOE CCD data retrieved 2026-09-19. The figure therefore holds only at the federal test's draw. A household that uses more or less hot water than the test assumes will use a different amount of gas. The steps behind the calculation are set out in how the annual cost is calculated.

Among the 397 models registered as a gas tankless unit at the high draw pattern, this unit ranks 229th lowest in energy use out of 397. That places it in the second-highest quarter of its class for energy use. Its 206 therms sits 24 therms above the class median of 182 therms. The listed maximum flow rate in gallons per minute is 4.2. The high draw pattern describes a larger household, or one where showers and laundry overlap, so the comparison applies to that kind of use. A reader who wants energy use at or below the class median would need to look at models ranked ahead of 229th. The water heater selector filters by fuel, space and size, and you can look up a same-class replacement by model number.

The registry does not state a running cost, and this page does not either. The cost depends on the state average residential gas price for the reader's ZIP, applied to the 206 therms at the high draw pattern. The cost calculator applies that price to this figure. Because the figure is 24 therms above the class median of 182 therms, the same gas price gives a higher yearly cost than a unit at the median would have at that draw. Actual gas use in a specific home is not available from the registry, so the computed figure is a test-based estimate, not a measurement. The modeled installed-cost range is shown in its own block with its source and date. It is not a quote and is not repeated here.