A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1)
A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) is a heat pump (hybrid electric) water heater from A. O. Smith with a 46 gallon rated tank and a 70 gallon first-hour rating at a 3.52 UEF — 923 kWh/yr certified use, 46.6 in tall.
Our take
Twenty-one catalog listings across 8 brand names — A. O. Smith, GSW, Giant, John Wood, and more — make this standard-height CO₂ split one of the most widely rebadged heat pumps certified. The spec explains the popularity: a 70-gallon first-hour rating above the class median, a compressor that works down to 1 °F (integrated rivals stop in the mid-30s), R-744 refrigerant with a GWP of 1, and a 46.6-inch tank that fits normal spaces. UEF is 3.52, a hair under the 3.55 median, at about $157 a year. Connected-capable, 240 V / 20.2 A.
Best for: Cold-climate installs wanting heat-pump savings year-round.
Trade-off: Two-piece installation; and the UEF sits fractionally below the class median.
Efficiency
Uniform Energy Factor (UEF)
3.52
Annual electricity use
923 kWh/yr
Recovery efficiency
429 %
General
Fuel
Electric
Capacity
First-hour rating
70 gal
Rated storage volume
46 gal
Draw pattern
Medium
Heat pump
Heat pump type
Split System HPWH
Refrigerant (GWP)
R-744 (CO₂) (GWP:1 | Lower GWP)
Compressor low-temp cutoff
1 °F
Installation
Input voltage
240
Max current draw
20.2 A
Smart features
Smart / connected capable
Yes
Dimensions
Height
46.6 in
Diameter
18 in
Certification
ENERGY STAR certified
Yes
Who is the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) for?
Its 70 gallon first-hour rating suits a
household of 3–4 people under DOE sizing guidance.
Estimated running cost: about $157/year at the national
average electricity rate (923 kWh/yr certified use).
Needs a 240 V circuit; at 20.2 A max draw plan for a 30 A breaker (NEC 125% continuous-load rule).
The heat pump compressor operates down to 1 °F ambient — below that, backup
elements take over.
Also sold as
The A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) is certified hardware that A. O. Smith and its partner brands
publish under 21 names. The same specifications apply to every
variant:
Is the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) ENERGY STAR certified?
Yes, the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) holds a current ENERGY STAR certification for water heating efficiency (UEF 3.52).
How much does the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) cost to run per year?
About $157 per year at national average energy rates, based on its certified annual energy use under the DOE test draw pattern. Your rate and usage change this figure.
What electrical circuit does the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) need?
The A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) runs on a 240 V circuit drawing up to 20.2 A; per the NEC 125% continuous-load rule plan for at least a 30 A breaker (check the installation manual for the required circuit).
Is the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) a smart water heater?
Yes, the A. O. Smith Split System Heat Pump 50-Gallon (HPACO-45 1-+AXST-50S 1) is connected-capable, with app control and eligibility for most utility demand-response programs.
