Rheem RTEX-08 Electric Tankless Water Heater 8 kW
- Capacity: 1.9 gallons
- Wattage: 8000 watts
- Power Source: Corded Electric
- Maximum Temperature: 140 °F
Last refreshed Sep 8, 2026 · Based on the Amazon listing and published specifications, not hands-on testing.
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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ASIN: B01N12VLI7Model: RTEX-08Category: Water Heaters
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.
Pros and cons
- 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 Depth | 12.6 inches |
| Item Dimensions W X H | 8.2 × 12.6 inches |
| Capacity & performance | |
| Capacity | 1.9 gallons |
| Maximum Temperature | 140 °F |
| Heat Output | 8 KW |
| Power & efficiency | |
| Wattage | 8000 watts |
| Power Source | Corded Electric |
| Voltage | 240 voltshigher than 78% of 38 water heaters |
| 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 warranty |
| Other details | |
| Maximum Pressure | 150 psi |
| Number Of Items | 1 |
| Style Name | Point-Of-Use, 8 Kw |
| Special Features | ON/OFF Dial Control and Adjustable Digital Temperature Display |
| Item Type Name | Water Heater |
Closest rivals on specs
Chronomite SR-20L/208 Instant-Flow Tankless Water Heater- Voltage 240 vs 208 volts (+15%)
Eemax LavAdvantage SPEX8208T Tankless Water Heater- Voltage 240 vs 208 volts (+15%)
EcoSmart ECO 8 Electric Tankless Water Heater- Item Depth 12.6 vs 4 inches (+215%)
Frequently asked questions
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?
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.