Water heaters
Tank, tankless and heat pump water heaters.
Buyer's guide: Water heaters: heat pump, tankless, or conventional tankWe hold full sourced data on 11 water heaters, each with a specification traced to its source and cross-checked against owner reports.
All the water heaters we have data on
Sorted by data completeness.
Rheem ProTerra Hybrid 50XE50T10HS45U0
The default heat pump water heater for most US households: 50 gallons, UEF 3.75, widely stocked and widely serviced.
Owners: 2 watch-out 2 reports →Rheem ProTerra Hybrid 80XE80T10HS45U0
80-gallon version of the ProTerra, UEF 4.0 — the highest efficiency in the mainstream heat pump water heater market.
Owners: 2 watch-out 2 reports →A.O. Smith ProLine XE Voltex ALHPTS-66
66-gallon heat pump water heater with a UEF of 4.02, the highest figure in our water heater set. Sold under A. O. Smith's 'ProLine XE Voltex AL / Smart Hybrid' line — a different, retail-exclusive 'Signature Series' name is used for a different model-number family at Lowe's, so don't cross-shop the names.
Owners: 1 watch-out2 mixed 4 reports →A.O. Smith ProLine XE Voltex ALHPTS-80
80-gallon version of the same ProLine XE Voltex AL 'Smart Hybrid' platform as the HPTS-66 — same compressor and control architecture, larger tank.
Owners: 1 watch-out 1 report →Bradford AeroTherm Series G2RE2HP5010-1NCTT
Bradford White's second-generation heat pump water heater, launched July 2025, with the ICON control system and app connectivity. The highest UEF in our catalogue at 3.89.
Owners: 1 watch-out 1 report →Bradford AeroTherm Series G2RE2HP8010-1NCTT
80-gallon version of the AeroTherm G2 platform. UEF 4.00, the joint-highest efficiency figure in our catalogue.
Bradford Defender Safety SystemRG250T6N
Bradford White's baseline pro-channel natural-gas tank, atmospheric vent, with the Defender flammable-vapor-resistant (FVIR) burner chamber. UEF 0.63 — confirmed as UEF, not an older Energy Factor rating, on Bradford White's own current spec sheet, though some retailers mislabel the same number 'EF'.
Owners: 1 good1 watch-out 2 reports →Navien NPE-A2NPE-240A2
Condensing gas tankless water heater, UEF 0.95, 11.2 GPM at a 35°F rise — Navien's mid-large residential model, ENERGY STAR certified.
Owners: 1 watch-out 1 report →Rheem MarathonMR50245C
Conventional resistance-element electric tank with a lifetime-warranted, non-metallic fiberglass tank — no compressor, no heat pump efficiency, but a tank that structurally can't rust through.
Owners: 1 watch-out 1 report →Rinnai RX SeriesRX160iN
Condensing gas tankless water heater, UEF 0.93, endless hot water with no standby loss.
Owners: 1 good1 watch-out1 mixed 4 reports →SANCO2 SANCO2 83 galGS4-45HPC + SAN-83SSAQA
Split-system CO2 refrigerant heat pump water heater rated to operate down to -25°F ambient, with a UEF of 3.75.
Owners: 1 good2 mixed 4 reports →What the specifications mean
UEF
Uniform Energy Factor -- the DOE-standard measure of water heater efficiency.
Values above 1.0 are only possible for heat pump water heaters, which move heat rather than create it. A UEF of 3.5 means the unit delivers 3.5 units of water heating per unit of electricity.
Tank capacity (gal)
Storage volume.
First hour rating (gal)
Gallons of hot water deliverable in the first hour starting from a full tank.
More useful than raw tank size for judging whether the household runs out of hot water.
Minimum ambient air temperature (°F)
Coldest surrounding air temperature at which a heat pump water heater runs in heat pump mode.
A heat pump water heater in an unconditioned garage in a cold climate spends the winter on resistance backup, which erases its efficiency advantage.