Explainers
Seven short pieces on reading the certified list: what each test figure means, why some numbers never compare, and what the data shows about types, brands and refrigerants. Every number comes from the list as of October 27, 2026.
- What a first-hour rating tells you, and what rated volume doesn’t
How the DOE first-hour rating differs from rated volume: medians per rated gallon for 120 certified heat-pump and gas storage rating sets.
- UEF explained: why heat pumps rate 2.52 to 4.50 and gas units 0.86 to 0.98
What the Uniform Energy Factor measures, why heat pumps and gas units sit on separate scales, and how UEF tracks rated energy within a draw pattern.
- Draw patterns, the hidden label behind every UEF
How the DOE assigns very small, low, medium and high draw patterns from first-hour rating or flow, and why 814 of 1,138 certified models test at high.
- Plug-in 120-volt vs 240-volt and split heat-pump water heaters: what the ratings show
Median UEF, first-hour output per rated gallon and rated kWh for 120-volt plug-in, 240-volt integrated and split-system heat-pump water heaters.
- Identical ratings, different brand names: rating sets shared across brands
1,005 of 1,138 certified water heater model numbers share their ratings with another brand. How the list reduces to 187 rating sets.
- Tankless max flow at a 67 °F rise: reading the GPM numbers
How DOE rates gas tankless water heaters by max flow at a 67 °F rise, and how certified flow tracks gas input from 130,000 to 199,000 Btu/h.
- Heat-pump compressor cut-off temperatures and refrigerants on the certified list
Listed compressor cut-off temperatures for 90 heat-pump water heater rating sets, by refrigerant: R-134a, CO2, R-1234yf, R-513A and R-32.