Mizudo FDG-CS120S vs Ranein RH8K-LPG: which uses less energy?
At the medium draw pattern the Mizudo FDG-CS120S uses 134 therms a year and the Ranein RH8K-LPG 135 — 2 therms (1%) less, about 16 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 | Ranein RH8K-LPG |
|---|---|---|
| UEF (Uniform Energy Factor) | 0.83 (better) | 0.82 |
| Energy use per year (therms) | 134 (better) | 135 |
| Max flow (GPM) | 3.3 | 3.6 |
| Installed cost range NLR REMDB | $1,792–$2,743 | $1,745–$2,687 |
| CPSC recall naming it CPSC | none on file | none on file |
DOE CCD · 2026-09-19 NLR REMDB · 2026-04-01 CPSC · 2026-09-24
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 above.
- No CPSC recall on file names either model (list checked 2026-09-24).
- 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 2 therms less a year on the same test.
- Pick the Ranein RH8K-LPG if you run more fixtures at once: it lists 3.6 GPM against 3.3.
- Neither if you need more than 3.6 GPM at the same time — neither unit lists more. Check how to size a tankless unit by GPM.
Each model on its own
- Mizudo FDG-CS120S 134 therms a year
- Ranein RH8K-LPG 135 therms a year