DoesTheMath

Kepler MGWH180IXNN vs RELIANCE WATER HEATERS ATHR-180M 1**: which uses less energy?

At the high draw pattern the Kepler MGWH180IXNN and the RELIANCE WATER HEATERS ATHR-180M 1** use the same energy, 178 therms a year each, on the same federal test. Both are filed as a gas tankless unit, so the comparison holds; what separates them is below. Enter your ZIP to price either one on your own rate.

Side by side

Compared within one class only: models filed as a gas tankless unit at the high draw pattern.

Filed and computed figures
Kepler MGWH180IXNN RELIANCE WATER HEATERS ATHR-180M 1**
UEF (Uniform Energy Factor) 0.95 0.95
Energy use per year (therms) 178 178
Max flow (GPM) 5.2 5.3
Installed cost range $2,358–$3,405 $2,358–$3,405
ENERGY STAR certified yes yes
On the market since 2024-05-30 2024-02-01
DOE CCD · 2026-09-19

What it costs to run

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.
  • 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 Kepler MGWH180IXNN since 2024-05-30, the RELIANCE WATER HEATERS ATHR-180M 1** since 2024-02-01. A sale date, not a lifespan.

Which should you pick?

  • Pick the Kepler MGWH180IXNN if its price or availability suits you — on energy the two are level.
  • Pick the RELIANCE WATER HEATERS ATHR-180M 1** if you run more fixtures at once: it lists 5.3 GPM against 5.2.
  • Neither if you need more than 5.3 GPM at the same time — neither unit lists more. Check how to size a tankless unit by GPM.

Each model on its own

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