A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 1)
A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 1) is a heat pump (hybrid electric) water heater from A. O. Smith with a 45 gallon rated tank and a 67 gallon first-hour rating at a 3.52 UEF — 923 kWh/yr certified use, 57 in tall.
Our take
A split-system design with a CO₂ (R-744) refrigerant — GWP of 1 versus 1,430 for the R-134a most of this class uses — and a compressor rated to operate down to 1 °F, where typical integrated units cut off around 35–37 °F. That makes it one of the few 40-gallon-class options whose heat pump keeps working through a real winter in an unconditioned space. UEF is 3.52, below the 3.73 cohort median, at about $157 a year; the 67-gallon first-hour rating clears the median. Six brand names sell this hardware. The indoor tank is a slim 16 inches across.
Best for: Cold garages and unconditioned spaces that defeat integrated heat pumps.
Trade-off: Split installation means an outdoor unit and refrigerant lines, not a drop-in swap.
Efficiency
Uniform Energy Factor (UEF)
3.52
Annual electricity use
923 kWh/yr
Recovery efficiency
413 %
General
Fuel
Electric
Capacity
First-hour rating
67 gal
Rated storage volume
45 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
57 in
Diameter
16 in
Certification
ENERGY STAR certified
Yes
Who is the A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 1) for?
Its 67 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 40-Gallon (HPACO-45 1-+AXST-50T 1) is certified hardware that A. O. Smith and its partner brands
publish under 14 names. The same specifications apply to every
variant:
Is the A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 1) ENERGY STAR certified?
Yes, the A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 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 40-Gallon (HPACO-45 1-+AXST-50T 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 40-Gallon (HPACO-45 1-+AXST-50T 1) need?
The A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 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 40-Gallon (HPACO-45 1-+AXST-50T 1) a smart water heater?
Yes, the A. O. Smith Split System Heat Pump 40-Gallon (HPACO-45 1-+AXST-50T 1) is connected-capable, with app control and eligibility for most utility demand-response programs.
