Rheem 8kW Multi Fixture Tankless Electric Water Heater
- Water Heater
- 1.9 gallons
- 8000 watts
- 8000 watts
Works well as a compact single-fixture tankless heater once installed and dialed in correctly, but buyers should plan for one fixture at a time rather than treating the multi-fixture label as simultaneous capacity.
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How it ranks among the 10 water heaters we track
4.1★ across 419 Amazon ratings, Bayesian-smoothed toward the category average.
419 Amazon ratings, weighted on a log scale so huge counts don't drown everything.
100+ bought on Amazon last month.
Brand identity, imagery, description and spec coverage.
The ProductDome score is separate from the Amazon rating shown above: it combines the Bayesian-smoothed Amazon rating with evidence volume, tracked demand, and data quality across the 10 water heaters we track - how the scorecard works · full water heaters data report. Confidence: high - strong rating volume and complete data.Updated 8 days ago. Data-computed, not a hands-on test. Compiled by the ProductDome Research Team.
Overview
The Rheem RTEX-08 is an 8kW, 240V tankless electric water heater rated for up to 1.95 gallons per minute, built to run on a 40-amp double-pole breaker and sized by Rheem for multiple fixture applications.
This is a hardwired, whole-circuit installation rather than a plug-in unit, requiring a 40-amp breaker, number 8 AWG copper wiring, and a household panel with at least 100 amps of service. Despite the multi-fixture label, several installers report it comfortably covers one shower or one sink at a time, and running two fixtures together strains its output, so it is realistic to plan around single-fixture use per heater. Digital thermostatic controls adjust in 1-degree steps from 80 to 140 Fahrenheit.
- 8kW, 240V tankless heater, up to 1.95 GPM
- Requires 40-amp double-pole breaker and #8 AWG wiring
- Digital thermostat, 80 to 140 degrees F in 1-degree steps
- 5-year leak, 1-year parts warranty
Who it's for
Suits an RV, small apartment, or single bathroom needing on-demand hot water from one shower or sink at a time, especially where space for a storage tank is not available. Less suited to a household expecting to run a shower and another fixture simultaneously without a flow limiter.
What buyers say
From Amazon customer reviews.
Buyers running it on a single fixture, an RV shower, a studio apartment bathroom, or one sink, generally report it heats reliably once installed and set up correctly, including one owner who has used it as a backup to an indirect tank system without noticing a difference. The most common install issue is the compression fitting size in the documentation being wrong, and more than one buyer had to turn the output valve down or add a flow limiter to stop temperature swings once a shower came on. One licensed electrician rated it far more harshly, saying it never got hot enough for a shower even at its highest setting, and another buyer's replacement unit failed in under four years versus six-plus years from an older Rheem model.
Strengths and trade-offs
Drawn from this product's published specifications.
- Compact 240V design frees up space versus a tank
- Handles a single shower or sink reliably
- Digital thermostat adjusts in 1-degree steps
- Straightforward install for anyone comfortable with 240V wiring
- Documentation lists the wrong compression fitting size
- Not strong enough for two fixtures at once
- One buyer's replacement failed sooner than the original
- Needs a flow limiter to avoid temperature swings
Performance notes
Output is controlled by a digital thermostat in 1-degree steps, but real-world flow also depends on turning down the output valve or adding a flow limiter, since running it wide open past what the unit can heat leads to fluctuating temperature. Installers also flag that the compression fitting size printed in the documentation does not match the actual 5/8 inch fitting on the unit, which caught more than one buyer off guard during install. Longevity reports are mixed, with one buyer's original Rheem lasting over six years and its RTEX-08 replacement failing in under four.
Specifications
| Brand | Rheem |
|---|---|
| Model | RTEX-08 |
| Dimensions & fit | |
| Item Dimensions W x H | 8.2 × 12.6 inches |
| Item Depth | 12.6 inches |
| Capacity & performance | |
| Capacity | 1.9 gallons |
| Heat Output | 8000 watts |
| Maximum Temperature | 140 °F |
| Power & efficiency | |
| Wattage | 8000 watts |
| Power Source | Corded electric |
| Voltage | 240 volts |
| Construction & materials | |
| Material Type | Stainless Steel |
| Color | Gray |
| Compatibility & installation | |
| Mount Type | Wall |
| Included components | |
| Unit Count | 1 |
| Included Components | Fittings, Aerators |
| Warranty & support | |
| Manufacturer Warranty Description | Limited lifetime |
| Other details | |
| Number of Items | 1 |
| Item Type Name | Water Heater |
| Special Features | ON/OFF Dial Control and Adjustable Digital Temperature Display |
| Style Name | Point-of-Use, 8 kw |
| Maximum Pressure | 150 psi |
How it compares
This product against the closest alternatives we track in water heaters.
| Product | Amazon rating | Ratings | ProductDome score |
|---|---|---|---|
| Rheem 8kW Multi Fixture Tankless Electric Water HeaterThis product | 4.1 / 5 | 419 | 4.0 / 5 |
| Stiebel Eltron 233219 2.5 gallonStiebel Eltron | 4.6 / 5 | 462 | 4.2 / 5 |
| CAMPLUX 5L Portable Tankless Water HeaterCamplux Enjoy Outdoor Life | 4.2 / 5 | 3,346 | 4.1 / 5 |
| EcoSmart ECO 8 Tankless Water HeaterEcoSmart | 4.2 / 5 | 709 | 4.0 / 5 |
| GASLAND BS158 Outdoor Portable Gas Water Heater 1.58GPMGasland | 4.3 / 5 | 1,400 | 3.9 / 5 |
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Questions about the Rheem RTEX-08
Common buyer questions answered straight from the product spec data - no fluff, no "it depends".
What electrical service does the Rheem RTEX-08 need?
It requires 240V single-phase power, a 40-amp double-pole breaker, number 8 AWG copper wiring with ground, and a panel with at least 100 amps of service.
Can the Rheem RTEX-08 run a shower and a sink at the same time?
Reviewers report it is better suited to one fixture at a time. Running more than one at once can strain its 1.95 GPM output.
What fitting size does the Rheem RTEX-08 actually use?
Despite documentation listing 1/2 inch compression fittings, buyers report the unit uses 5/8 inch compression fittings, which needs different connectors than expected.