A. O. Smith T-H3M-OS-N 1**
A. O. Smith T-H3M-OS-N 1** is in the DOE listing as of Oct 26, 2026.
It has a certified UEF of 0.91 and a certified flow of 3.5 gal/min at a 67°F rise.
Its certified flow is 3.5 gal/min at a 67°F rise, while A. O. Smith advertises 6.6 gal/min, no rise stated (Read Oct 5, 2026), so a comparison at the same rise is not possible.
- Gas tankless water heater
- 2 listed models
Not listed as ENERGY STAR certified on Oct 26, 2026.
Certified and advertised figures
- Flow at a 67°F rise
- 3.5gallons per minuteCertified
- Advertised flow
- 6.6gallons per minuteA. O. Smith, no rise stated
- UEF
- 0.91Uniform energy factor
Your fixtures at once
Change your hour and flowFlow where you live
Colder incoming water needs a bigger rise, so the heater gives less flow.
- Cold water
- Cold water must be at least 10°F colder than the hot water setting.
- Flow estimate
- The estimate uses the lowest certified flow among the listed models. It is about 3.4 gal/min at a 70°F rise.
Flow limits
- The estimate excludes the flow needed to turn the heater on, heat lost in pipes, and installation.
- Cold water from a well or long pipe run can differ from the temperature you enter.
- Without a stated flow limit, estimates for warmer water may exceed the heater’s actual flow.
Advertised and certified figures
| Figure | Advertised | Certified | Advertiser | Read |
|---|---|---|---|---|
| UEF | 0.91 | 0.91 | A. O. Smith | Read Oct 5, 2026 |
| UEF | up to 0.91 | 0.91 | A. O. Smith | Read Oct 5, 2026 |
| Flow | 6.6 gal/min, no rise stated | 3.5 gal/min at a 67°F rise | A. O. Smith | Read Oct 5, 2026 |
| Flow | up to 6.6 gal/min, no rise stated | 3.5 gal/min at a 67°F rise | A. O. Smith | Read Oct 5, 2026 |
| Flow | 3.5 gal/min at a 67°F rise | 3.5 gal/min at a 67°F rise | A. O. Smith | Read Oct 5, 2026 |
Certified figures by listed model
| Model number | UEF | Flow at a 67°F rise (gal/min) | Recovery efficiency | Draw pattern |
|---|---|---|---|---|
| ATO-140H 1** | 0.91 | 3.5 | 96% | Medium |
| ATO-140H 1*1 | 0.91 | 3.5 | 96% | Medium |
UEF is the uniform energy factor. A dash means the model has no such figure.
It heats 3.5 gallons per minute of water by 67°F in the test. The gas tankless type has a median flow of 4.8 gallons per minute. Among 487 gas tankless models, 426 give more flow at a 67°F rise.
It was not listed as ENERGY STAR certified on Oct 26, 2026. In tests, 91% of the energy it uses ends up as hot water (UEF 0.91). In the test, daily hot water use was set to medium (its draw pattern). Of 77 gas tankless models with the same draw pattern, 2 have a higher UEF. A UEF of 0.82 is the median for its type and draw pattern. While it heats water, 96% of the energy used goes into the water (its recovery efficiency).
It is sold as ATO-140H 1** and ATO-140H 1*1. Its test figures match those of 5 other basic models. Each of them is listed under a different brand.
It may qualify for 2 rebate programs in 2 states. Another 2 programs may accept it if it meets their other terms.
Also listed as
They carry every figure in the table above.
Rebates
| Program | State | Status | Program page |
|---|---|---|---|
| SoCalGas High-Efficiency or ENERGY STAR Certified Natural Gas Tankless Water Heaters rebate | CA | May qualify if it meets the other terms | Its own page |
| Xcel Energy MINNESOTA RESIDENTIAL ENERGY EFFICIENCY PROGRAMS (gas storage, gas tankless) | MN | May qualify | Its own page |
| PSE&G Tankless Water Heaters | NJ | May qualify | Its own page |
| Focus on Energy (gas tankless) | WI | May qualify if it meets the other terms | Its own page |
Programs change their terms. Check the program's own page before you buy.
- Every A. O. Smith basic model
- Every gas tankless water heater certified below 4.0 gallons per minute
- Every gas tankless water heater
- The most-searched gas tankless models side by side
Not covered
- Changes to an advertised figure after the date beside it.