Heat pump water heaters are the single most cost-effective energy upgrade most homeowners can make today. They use a refrigerant loop to pull heat from ambient air into the water — using roughly 70% less electricity than a traditional electric resistance tank. The A.O. Smith Voltex PHPT-50 and Rheem ProTerra PROPH50 are the two machines that come up most often when an HVAC or plumbing contractor recommends a heat pump water heater. Both are 50-gallon tanks. Both are excellent. The right choice depends on your basement temperature and noise tolerance.

Specs Comparison

How Heat Pump Water Heaters Work — And Why It Matters

Both units operate like a refrigerator in reverse — they extract heat from ambient air and pump it into the water tank, then exhaust cooler, dehumidified air back into the room. In heat pump mode, both machines use roughly 1 kWh of electricity to produce 3–4 kWh of heat. A traditional electric resistance heater converts 1 kWh to 1 kWh — the efficiency difference is three to four times.

Both units have backup electric resistance elements that activate when hot water demand exceeds what the heat pump can supply, or when ambient temperature is too cold for efficient heat pump operation. The switchover is automatic and transparent to the user.

The catch: both units extract heat from the surrounding air, which means they cool and dehumidify the space they're installed in. In a cold basement, this is fine — in an air-conditioned living space, it adds cooling load in summer. Install in an unconditioned basement or garage for best results.

Efficiency and First-Hour Rating

The Rheem ProTerra PROPH50 achieves a UEF of 4.0 in heat pump mode — the highest efficiency rating among mainstream 50-gallon heat pump water heaters. The A.O. Smith Voltex PHPT-50 achieves a UEF of 3.45. Both are dramatically better than the ~0.95 UEF of a condensing gas water heater or the ~0.92 of a traditional electric tank.

First-hour rating — how much hot water the unit can deliver in the first hour from a full tank — is 63 gallons for the Rheem ProTerra and 65 gallons for the A.O. Smith Voltex. Essentially identical for household planning purposes.

At average U.S. electricity rates and typical hot water usage, a heat pump water heater saves $400–$500/year versus a standard electric resistance tank. Both units qualify for the federal 30% energy efficiency tax credit, which at the installed cost of $1,500–$2,000 represents a significant return.

Cold-Climate Performance and Operating Range

This is where A.O. Smith has a meaningful advantage. The Voltex PHPT-50 operates in heat pump mode down to 37°F ambient temperature. The Rheem ProTerra operates in heat pump mode down to 40°F. That 3°F difference might seem trivial, but unheated basements in New England and the upper Midwest can drop below 40°F in January — at which point the Rheem switches to resistance heat and loses its efficiency advantage.

If your installation space stays above 40°F year-round, this distinction doesn't matter. If your basement or garage sees winter temperatures in the 37–42°F range, A.O. Smith's lower operating threshold is a practical advantage that translates directly to lower electricity bills.

Both units have multiple operating modes — heat pump only, hybrid (heat pump + resistance as needed), resistance-only, and vacation mode. Neither requires any user intervention once set up; the hybrid mode handles everything automatically.

Noise, Smart Features, and Installation

Heat pump water heaters are louder than standard electric tanks — the compressor and fan make noise. The A.O. Smith Voltex runs at approximately 49 dBA. The Rheem ProTerra runs at approximately 49–52 dBA depending on operating mode. Both are louder than a standard tank but acceptable in a basement installation away from living spaces.

Rheem's EcoNet smart features are slightly more polished than A.O. Smith's app — scheduling, efficiency tracking, and vacation mode are all easier to configure. Rheem's LeakGuard leak detection, which shuts off the water supply if a leak is detected, is a standout feature not available on the A.O. Smith at base models.

Both units are 50 gallons and roughly 62 inches tall with top connections — verify ceiling height in your installation space. Both require a 240V / 30A circuit. Installation typically costs $500–$1,000 beyond the appliance cost depending on existing wiring and plumbing configuration.

Best For

• a: Cold-climate homeowners with basements that drop below 40°F in winter, or anyone where compressor noise levels are a concern
• b: Most homeowners who want maximum efficiency and smart leak protection in a basement that stays above 40°F year-round

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