A. O. SMITH GUF-40 1** vs Rheem PROG39S-38U RH62 EC1*: which uses less energy?
At the medium draw pattern the A. O. SMITH GUF-40 1** uses 171 therms a year and the Rheem PROG39S-38U RH62 EC1* 188 — 17 therms (9%) less, about 173 therms over ten years. Both are filed as a gas tank, 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 tank at the medium draw pattern.
| Figure | A. O. SMITH GUF-40 1** | Rheem PROG39S-38U RH62 EC1* |
|---|---|---|
| UEF (Uniform Energy Factor) | 0.65 (better) | 0.59 |
| Energy use per year (therms) | 171 (better) | 188 |
| First hour rating (gal) | 68 | 68 |
| Rated storage volume (gal) | 38 | 37 |
| Installed cost range | $1,702–$2,914 | not published |
| 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 A. O. SMITH GUF-40 1** if running cost matters most: it uses 17 therms less a year on the same test.
- Pick the Rheem PROG39S-38U RH62 EC1* 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 GUF-40 1**.
- Neither if your household's busiest hour needs more than 68 gallons of hot water — neither lists more. Check whether a 40-gallon heater is enough.
Each model on its own
-
A. O. SMITH GUF-40 1**
Its filed figures, class position and running cost on your ZIP.
-
Rheem PROG39S-38U RH62 EC1*
Its filed figures, class position and running cost on your ZIP.