A. O. Smith TK-110U-E 2**
A. O. Smith TK-110U-E 2** is in the DOE listing as of Oct 26, 2026.
It has a certified UEF of 0.81 and a certified flow of 3.5 gal/min at a 67°F rise.
Its advertised flow of 3.5 gal/min at a 67°F rise from A. O. Smith matches the certified 3.5 gal/min at a 67°F rise (Read Oct 5, 2026).
- 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
- 3.5gallons per minuteA. O. Smith, up to, no rise stated
- UEF
- 0.81Uniform energy factor
Your fixtures at once
Change your hour and flowFlow where you live
A bigger rise from colder incoming water leaves the heater with 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 | 0.81 | 0.81 | A. O. Smith | Read Oct 5, 2026 |
| UEF | up to 0.81 | 0.81 | 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 |
| Flow | up to 3.5 gal/min, no rise stated | 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-110U 2** | 0.81 | 3.5 | 83% | Medium |
| GT15-110U-O 2** | 0.81 | 3.5 | 83% | Medium |
UEF is the uniform energy factor. A dash means the model has no such figure.
At a 67°F rise, its flow in the test is 3.5 gallons per minute. The gas tankless type has a median flow of 4.8 gallons per minute. Of 487 gas tankless models, 426 have a higher flow than this one.
It was not listed as ENERGY STAR certified on Oct 26, 2026. In tests, 81% of the energy went to hot water, so its UEF is 0.81. In the test, daily hot water use was set to medium (its draw pattern). Of 77 gas tankless models with the same draw pattern, 48 have a higher UEF. On its draw pattern, the median gas tankless UEF is 0.82. Of the energy it spends heating water, 83% ends up in it (its recovery efficiency).
Its 2 model numbers are ATO-110U 2** and GT15-110U-O 2**. There are 6 more basic models with the same test figures. They are listed under 6 other brands, one each.
Also listed as
They carry every figure in the table above.
- 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.