Rheem ECO18
Rheem ECO18 is in the DOE listing as of Oct 26, 2026.
It has a certified UEF of 0.94 and a certified flow of 1.7 gal/min at a 67°F rise.
Its certified flow is 1.7 gal/min at a 67°F rise, while Rheem advertises 4.4 gal/min, no rise stated (Read Oct 4, 2026), so a comparison at the same rise is not possible.
- Electric tankless water heater
- 3 listed models
ENERGY STAR certification does not cover this type of water heater.
Certified and advertised figures
- Flow at a 67°F rise
- 1.7gallons per minuteCertified
- Advertised flow
- 4.4gallons per minuteRheem, no rise stated
- UEF
- 0.94Uniform energy factor
Your fixtures at once
Change your hour and flowFlow where you live
The heater gives less flow when colder incoming water needs a bigger rise.
- 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 1.6 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 |
|---|---|---|---|---|
| Flow | 4.4 gal/min, no rise stated | 1.7 gal/min at a 67°F rise | Rheem | Read Oct 4, 2026 |
| Flow | 3.2 gal/min, no rise stated | 1.7 gal/min at a 67°F rise | Rheem | Read Oct 4, 2026 |
| Flow | up to 3.51 gal/min, no rise stated | 1.7 gal/min at a 67°F rise | The Home Depot | Archived copy, Aug 21, 2024 |
Certified figures by listed model
| Model number | UEF | Flow at a 67°F rise (gal/min) | Recovery efficiency | Draw pattern |
|---|---|---|---|---|
| RETEX-18 | 0.94 | 1.7 | 98% | — |
| RMTEX-18 | 0.94 | 1.7 | 98% | — |
| RTEX-18 | 0.94 | 1.7 | 98% | — |
UEF is the uniform energy factor. A dash means the model has no such figure.
It warms 1.7 gallons per minute of water from 58°F to 125°F in the test. The median flow among electric tankless models is 0.7 gallons per minute. Among 337 electric tankless models, 40 give more flow at a 67°F rise.
In the test, 6% of its energy does not reach the hot water (UEF 0.94). Of the energy it spends heating water, 98% ends up in it (its recovery efficiency).
It is the basic model for RETEX-18, RMTEX-18, and RTEX-18. All of its test figures are shared by 2 other basic models. Those basic models are sold with ECOSMART and EEMAX as their brand names.
Also listed as
They carry every figure in the table above.
- Every Rheem basic model
- Every electric tankless water heater certified at 1.0 to 1.9 gallons per minute
- Every electric tankless water heater
Not covered
- Changes to an advertised figure after the date beside it.