DoesTheMath

ARISTON AURES SM 6.5 240V US* vs Rheem SPEX75T: which uses less energy?

At the very small draw pattern the Rheem SPEX75T uses 609 kWh a year and the ARISTON AURES SM 6.5 240V US* 615 — 6 kWh (1%) less, about 63 kWh over ten years. Both are filed as an electric tankless unit, 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 tankless unit at the very small draw pattern.

Filed and computed figures
ARISTON AURES SM 6.5 240V US* Rheem SPEX75T
UEF (Uniform Energy Factor) 0.96 0.97 (better)
Energy use per year (kWh) 615 609 (better)
Max flow (GPM) 0.7 0.7
Installed cost range $1,306–$1,838 $1,309–$1,862
ENERGY STAR certified not matched not matched
DOE CCD · 2026-09-19

What it costs to run

ARISTON AURES SM 6.5 240V US*: 615 kWh a year Rheem SPEX75T: 609 kWh a year

ARISTON AURES SM 6.5 240V US* — 615 kWh a year Rheem SPEX75T — 609 kWh a year

Rheem SPEX75T is 6 kWh a year lower than ARISTON AURES SM 6.5 240V US*.

DOE CCD · 2026-09-19

Report an issue with this number

Enter your ZIP to price both units on the same rate where you live.

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.
  • The actual warranty term is printed in each model’s documentation, not in any registry.

Which should you pick?

  • Pick the Rheem SPEX75T if running cost matters most: it uses 6 kWh less a year on the same test.
  • Pick the ARISTON AURES SM 6.5 240V US* if it is the one you can get installed sooner or for less — on the filed figures it has no advantage over the Rheem SPEX75T.
  • Neither if you need more than 0.7 GPM at the same time — neither unit lists more. Check how to size a tankless unit by GPM.

Each model on its own

Analytics cookies

We count page views without cookies for everyone, and that counter is what we use to decide what to build. Google Analytics is separate: it uses cookies to record how a page was used, and it loads only if you allow it. Decline and the site works exactly the same. What we collect.