DoesTheMath

A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** vs RINNAI REHP50BM: which uses less energy?

At the medium draw pattern the RINNAI REHP50BM uses 866 kWh a year and the A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** 915 — 49 kWh (5%) less, about 488 kWh over ten years. Both are filed as an electric tank, so the comparison holds. Enter your ZIP below to price the difference.

Side by side

Compared within one class only: models filed as an electric tank at the medium draw pattern.

Filed and computed figures
A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** RINNAI REHP50BM
UEF (Uniform Energy Factor) 3.55 3.75 (better)
Energy use per year (kWh) 915 866 (better)
First hour rating (gal) 72 73
Rated storage volume (gal) 48 46
Installed cost range $3,099–$4,228 $3,057–$4,409
ENERGY STAR certified yes yes
Sound level (dB) not filed 49
Refrigerant R-744 (CO2), GWP 1 R-134a, GWP 1430
On the market since 2026-02-13 2024-04-01
DOE CCD · 2026-09-19

What it costs to run

A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1**: 915 kWh a year RINNAI REHP50BM: 866 kWh a year

A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** — 915 kWh a year RINNAI REHP50BM — 866 kWh a year

RINNAI REHP50BM is 49 kWh a year lower than A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1**.

DOE CCD · 2026-09-19

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Reliability

Not published: Reliability, failure rates and each model’s actual warranty term.

The registries these figures come from certify energy performance under a federal test; none of them records how long a unit lasts or how often it fails, so this page does not rank the two on reliability.

What is here instead:

  • The filed efficiency, capacity and tank size of both models, side by side below.
  • Both are ENERGY STAR certified, which requires a manufacturer warranty of at least six years; the actual term for each model is not published.
  • Time on the market, as filed with ENERGY STAR: the A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** since 2026-02-13, the RINNAI REHP50BM since 2024-04-01. A sale date, not a lifespan.

Which should you pick?

  • Pick the RINNAI REHP50BM if running cost matters most: it uses 49 kWh less a year on the same test.
  • Pick the A. O. SMITH HPACO-45 1**+AXST-50LBTTP 1** if it is the one you can get installed sooner or for less — on the filed figures it has no advantage over the RINNAI REHP50BM.
  • Neither if your household's busiest hour needs more than 73 gallons of hot water — neither lists more. Check whether a 50-gallon heater is enough.

Each model on its own

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