A. O. Smith T-H3M-OS-N 1** vs Noritz NRC661A-DV-NG: which uses less energy?
An asterisk in a model number stands for any character: one filing covers several variants.
At the medium draw pattern the A. O. Smith T-H3M-OS-N 1** uses 122 therms a year and the Noritz NRC661A-DV-NG 125 — 3 therms (2%) less, about 27 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 | A. O. Smith T-H3M-OS-N 1** | Noritz NRC661A-DV-NG |
|---|---|---|
| UEF (Uniform Energy Factor) | 0.91 (better) | 0.89 |
| Energy use per year (therms) | 122 (better) | 125 |
| Max flow (GPM) | 3.5 | 3.4 |
| Installed cost range NLR REMDB | $2,169–$3,184 | $2,075–$3,074 |
| 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 A. O. Smith T-H3M-OS-N 1** if running cost matters most: it uses 3 therms less a year on the same test.
- Pick the Noritz NRC661A-DV-NG if it is the one you can get installed sooner or for less — on the filed figures it has no advantage over the A. O. Smith T-H3M-OS-N 1**.
- Neither if you need more than 3.5 GPM at the same time — neither unit lists more. Check how to size a tankless unit by GPM.
Each model on its own
- A. O. Smith T-H3M-OS-N 1** 122 therms a year
- Noritz NRC661A-DV-NG 125 therms a year