The first thing that struck me about the Rheem RTEX-24 24kW 240V Electric Tankless Water Heater wasn’t just its powerful output but how effortlessly it handled multiple hot water demands during testing. I was surprised by its precise digital temperature control, allowing adjustments in 1-degree increments, which really improves comfort. Its performance was steady even in colder climates, though I noted the importance of proper electrical capacity, since it requires 3 x 40 AMP double pole breakers and a 200 AMP service.
Compared to the Rheem 18kW model, the RTEX-24 delivers significantly higher flow rate potential—up to 5 GPM—making it ideal for larger homes or simultaneous uses like showers and appliances. While the 18kW version is easier to install and has a sleek LED display, the RTEX-24’s robust capacity ensures reliable hot water even at colder water temperatures. After hands-on testing and analyzing all specs, I recommend the Rheem RTEX-24 24kW 240V Electric Tankless Water Heater for its impressive combination of power, precision, and future-proof performance. It truly stands out in providing consistent hot water over a wide range of conditions.
Top Recommendation: Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
Why We Recommend It: This model offers a higher flow rate—up to 5 GPM—compared to the 4.4 GPM of the 18kW version, making it perfect for larger households or simultaneous use. Its adjustable digital temperature control allows for precise 1-degree increments, ensuring comfort and energy efficiency. The proven performance across different water temperatures makes it reliable, even in colder climates, which gave me confidence during testing.
Best 10 gpm electric tankless water heater: Our Top 2 Picks
- Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray – Best high-capacity electric tankless water heater
- Rheem 18kW 240V Tankless Electric Water Heater, Gray – Best energy-efficient electric tankless water heater
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
- ✓ Quiet operation
- ✓ Precise temperature control
- ✓ Space-saving design
- ✕ Requires high electrical capacity
- ✕ Difficult to install without upgrades
| Electrical Power | 24 kW (24,000 watts) |
| Voltage | 240V |
| Current Rating | 100A |
| Breaker Requirements | 3 x 40 AMP double pole breakers |
| Flow Rate Capacity | Up to 10 GPM (gallons per minute) depending on water temperature and conditions |
| Temperature Range | 80°F to 140°F with 1-degree adjustment increments |
Imagine flipping the switch on this Rheem RTEX-24 and being greeted not just with hot water, but with a surprising silence. I expected a loud hum or some vibration, but it runs almost whisper-quiet, which caught me off guard.
The sleek, gray exterior feels sturdy and modern, fitting seamlessly into a utility closet or basement corner.
Handling the unit, I noticed how compact yet robust it is. It’s pretty hefty, but the mounting brackets make installation straightforward.
The digital temperature display is bright and easy to read, and tweaking the water temperature in 1-degree increments feels precise. Turning the dial control feels smooth, and the auto shut-off when not in use adds a nice touch of safety.
Once connected, I was impressed by how consistently it delivered hot water, even with multiple fixtures running. The power requirements are significant—make sure your home can handle 200 amps and that your breaker panel has enough space.
The unit heats water on demand, which means no standby heat loss, saving energy over traditional tanks.
In real-world use, I found the flow rate maintained well in moderate cold water conditions, making it ideal for larger households or small commercial setups. The unit’s efficiency is noticeable—no venting needed, and it heats only as needed, reducing energy bills.
The only downside? It’s a bit of a beast to install if your electrical panel isn’t already prepared for such a high load.
Rheem 18kW 240V Tankless Electric Water Heater, Gray
- ✓ Precise digital temperature control
- ✓ Easy installation and maintenance
- ✓ Reliable flow rate for most homes
- ✕ Not suitable for very high flow demands
- ✕ Slightly pricey compared to basic models
| Heating Element Material | Copper immersion elements |
| Power Rating | 18 kW |
| Voltage | 240 V |
| Flow Rate | up to 4.4 GPM |
| Temperature Control | External digital thermostat with LED display (+/- 1 degree accuracy) |
| Water Connection Size | Bottom 3/4 inch NPT threaded connections |
The moment I unboxed the Rheem 18kW 240V tankless electric water heater, I immediately noticed its sleek gray finish and compact design. It’s surprisingly lightweight, making it easier to handle than I expected for its power capacity.
The digital LED display caught my eye right away, with its clear readout and straightforward controls.
Installing it was straightforward—those bottom 3/4 inch NPT connections lined up perfectly, and the instructions were easy to follow. Once mounted and connected, I turned it on and was impressed by how quickly the digital thermostat responded.
The control offers precise temperature adjustments, with just a plus or minus 1-degree accuracy, which is perfect for avoiding sudden temperature swings.
The self-modulation feature is a game-changer. It adjusts power draw based on hot water demand, so I didn’t experience any sudden drops in pressure or temperature.
I tested it with multiple fixtures running simultaneously, and it maintained a steady flow rate of up to 4.4 GPM without any hiccups.
The copper immersion heating elements felt sturdy and field-serviceable, giving me confidence about long-term durability. Plus, the ability to easily replace parts if needed is a big plus.
Overall, it’s quiet during operation, and I appreciated how it seamlessly integrated into my existing setup without complicated wiring or plumbing issues.
For anyone looking for a reliable, high-capacity electric tankless heater, this model delivers consistent hot water and smart performance. Sure, it’s not meant for extremely high flow needs, but for a typical household, it hits the mark perfectly.