Mizudo FDG-CS120S vs RINNAI RE140E (REU-VE1720WD-US): which uses less energy?
At the medium draw pattern the Mizudo FDG-CS120S uses 134 therms a year and the RINNAI RE140E (REU-VE1720WD-US) 137 — 3 therms (2%) less, about 33 therms over ten years. Both are filed as a gas 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 a gas tankless unit at the medium draw pattern.
| Figure | Mizudo FDG-CS120S | RINNAI RE140E (REU-VE1720WD-US) |
|---|---|---|
| UEF (Uniform Energy Factor) | 0.83 (better) | 0.81 |
| Energy use per year (therms) | 134 (better) | 137 |
| Max flow (GPM) | 3.3 | 3.2 |
| Installed cost range | $1,792–$2,743 | $1,698–$2,632 |
| ENERGY STAR certified | not matched | not matched |
What it costs to run
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 Mizudo FDG-CS120S if running cost matters most: it uses 3 therms less a year on the same test.
- Pick the RINNAI RE140E (REU-VE1720WD-US) if it is the one you can get installed sooner or for less — on the filed figures it has no advantage over the Mizudo FDG-CS120S.
- Neither if you need more than 3.3 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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Mizudo FDG-CS120S
Its filed figures, class position and running cost on your ZIP.
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RINNAI RE140E (REU-VE1720WD-US)
Its filed figures, class position and running cost on your ZIP.