Rheem Performance RTEX-36 Tankless Water Heater
- 36 kW heat output, self-modulating
- Flow rate shown as 6 gpm in the title and 8.8 gpm in the specs
- 140 °F maximum temperature
- UEF up to .94, digital thermostatic controls
- Wall mount, 21.62 in wide, 18.25 in tall, 3.5 in deep
- 19 lb unit weight
Last refreshed Sep 28, 2026 · Based on the Amazon listing and published specifications, not hands-on testing.
A high output electric tankless heater with digital temperature control and a self modulating design. The data conflicts on flow rate and omits electrical supply needs, so verify both with the seller.
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ASIN: B0785TV3HVModel: RETEX-36Category: Water Heaters
Overview
Rheem builds this heater as a wall mounted electric tankless heater that adjusts its output to match demand. Digital thermostatic controls hold the set temperature, and the unit is listed for indoor installation.
Choose it where a large electric heater can serve several fixtures with no gas line. The limitation is the sparse and conflicting data, since the flow rate varies across the listing and no voltage or breaker needs are given.
Who it's for
An owner planning an electric whole home or multi fixture upgrade with an electrician. The self modulating design adjusts power to the flow. Anyone on a limited panel should confirm the supply needs before ordering.
Pros and cons
- Self modulating output
- Digital temperature controls
- Wall mount design
- High efficiency factor listed
- Flow rate figures conflict
- Voltage and amperage not listed
- Capacity entry looks unreliable
Performance notes
A self modulating electric heater varies its power draw with the flow, so the temperature rise depends on incoming water temperature, flow and kilowatts available. The thermostat aims to maintain your chosen setting. With the flow rate unclear, real capacity should be checked before sizing.
Where it stands among water heaters
- #7 most-searched brand and model of the 24 water heaters lines we track (by search demand, not sales).
From the specs of the 55 water heaters we list; not a test result.
Specifications
| Brand | Rheem |
|---|---|
| Model | RETEX-36 |
| Dimensions & fit | |
| Item Depth | 3.5 inches |
| Item Dimensions W X H | 21.62"W x 18.25"H |
| Item weight | 19 pounds |
| Capacity & performance | |
| Flow Rate | 8.8 gpm (title shows 6 GPM)higher than 90% of 22 water heaters |
| Maximum Temperature | 140 °F |
| Wattage | 36 KW |
| Heat Output | 36 KW |
| Capacity | 6 gallons |
| Power & efficiency | |
| Power Source | AC |
| Construction & materials | |
| Color | Gray |
| Compatibility & installation | |
| Mount type | Wall |
| Included components | |
| Included Components | 683089 8 GPM ELEC TNKLSS |
| Unit Count | 1 Count |
| Other details | |
| Style Name | Indoor Installation |
| Special Features | Digital Thermostatic Temperature Controls, UEF up to .94 |
Closest rivals on specs
Titan N-180 Tankless Water Heater 18 kW- Flow Rate 8.8 vs 7 gpm (+26%)
- Item Depth 3.5 vs 4.5 inches (-22%)
ThermoMate ET180 Electric Tankless Water Heater 18 kW- Flow Rate 8.8 vs 4.4 gpm (+100%)
- Item Depth 3.5 vs 3.1 inches (+13%)
Rinnai V53DeP Propane Tankless Water Heater- Flow Rate 8.8 vs 5.3 gpm (+66%)
- Item Depth 3.5 vs 7.9 inches (-56%)
Frequently asked questions
How do I set the temperature on the Rheem RETEX-36?
The listing says it has digital thermostatic temperature controls and a 140 degree Fahrenheit maximum. It gives no step by step setup instructions.
What is the flow rate of the Rheem RETEX-36?
The listing is inconsistent, showing 6 gpm in the title, 8.8 gpm in the specs and 8 gpm in the description line.
Does the Rheem RETEX-36 need gas?
No. It is an electric tankless heater.