A plumber friend of mine keeps a laminated spec sheet taped inside his van because customers ask the same three questions every single time: how much power does it need, how much hot water will it actually give me, and will it fit where my old tank used to sit. Those three questions cover almost everything that matters about the RTEX-24, so let’s walk through the real specs instead of the marketing version.
The Rheem RTEX-24 is a 24kW, 240-volt electric tankless water heater with a maximum flow rate of 5.9 GPM, three copper immersion heating elements, and a physical footprint of roughly 18.25 inches tall by 17.63 inches wide. It requires three 40-amp double-pole breakers and Rheem recommends 200-amp household electrical service to run it safely.
Full Spec Sheet
Here’s the complete spec breakdown, pulled directly from Rheem’s official product listing:
| Spec | Detail |
|---|---|
| Power | 24 kW at 240V |
| Max flow rate | Up to 5.9 GPM |
| Fixtures served (max) | 2 showers, 2 sinks |
| Height | 18-1/4” |
| Width | 17-5/8” |
| Depth | 3-1/2” |
| Ship weight | 17.8 lbs |
| Water connections | 3/4” NPT |
| Breakers required | 3 x 40 AMP double pole |
| Household service recommended | 200 AMP |
| Temperature range | 80 to 140degF, adjustable in 1degF increments |
| Display | LED digital temperature display |
What “24kW” Actually Means for Your Hot Water
The kilowatt rating tells you how much electrical power the unit can draw to heat water, not how much hot water it produces on its own. More kW means the unit can raise the water temperature faster, which in turn supports a higher flow rate. That’s why the RTEX-24 outperforms the smaller RTEX-18 (18kW, 4.4 GPM max) despite both units using the same basic technology.
Rheem’s own spec sheet notes the RTEX-24 provides up to 5.9 GPM “in warm climates,” and that’s an important qualifier. Flow rate on any electric tankless heater depends on how much the incoming water temperature needs to rise to reach your set point. Warmer groundwater needs less of a temperature boost, so the same unit delivers more usable flow. In colder climates, expect a lower effective GPM even though the unit itself hasn’t changed.
The Three-Element Design
The RTEX-24 uses three separate copper immersion heating elements rather than one large element. This matters for two reasons. First, it enables self-modulation, the unit only activates as many elements as needed for the current demand, rather than running at full power for a single faucet. Second, it means a single element failure doesn’t necessarily take the whole unit offline, since the other two can often still provide reduced hot water while you wait for a replacement part.
Real owner reviews on Amazon reflect both sides of this design. Several reviewers describe replacing a single failed element as a straightforward 30-minute repair: cut the breaker, shut off water, unscrew four wires, swap the element, and reconnect. Others report the elements failing repeatedly within the first year, in one detailed case (a verified purchase review from January 2021, updated over two years) a reviewer described replacing “every single part” of an 18kW unit before ultimately replacing the entire heater. This isn’t universal, but it’s a documented pattern worth knowing about before you buy, especially in homes with hard water that accelerates scale buildup on the elements.
Physical Size and Installation Footprint
At 18.25 inches by 17.63 inches and just 3.5 inches deep, the RTEX-24 mounts flat against a wall and takes up dramatically less space than a traditional 40 to 50 gallon storage tank. Rheem markets this as up to 93% smaller than a comparable tank unit, which tracks given a standard 50-gallon tank is roughly 60 inches tall and 20+ inches in diameter.
The unit connects via 3/4 inch NPT fittings at the bottom, and one verified reviewer specifically noted needing to use larger diameter piping (1 inch) between the electrical panel and the unit itself, not for water, but to physically fit the nine 8-gauge wires required for the three double-pole breaker circuits. That’s a detail most spec sheets don’t mention but matters for anyone planning their own electrical rough-in.
Temperature Control
The RTEX-24 uses an external digital display with a dial control, adjustable in 1-degree increments from 80 to 140degF. Multiple reviewers confirm the displayed temperature matches what actually comes out of the tap fairly closely, with one detailed review measuring a 2 to 4 degree drop at the fixture furthest from the unit, which is a normal and expected result of heat loss over pipe distance, not a defect.
What the Specs Don’t Tell You
Rheem’s own installation notes state plainly: “Ensure your home can accommodate the power supply and that enough space is available in your breaker panel for this unit.” That single sentence is doing a lot of work. It means the spec sheet numbers only matter if your actual electrical panel has room and capacity, something no online spec comparison can confirm for you. If you’re unsure, this is worth a call to a licensed electrician before you commit to buying, not after.
For the full sizing conversation, including how the RTEX-24 compares to other models in the lineup, see our RTEX-24 vs RTEX-18 sizing guide.
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater - View Full Specs on Amazon
The Bottom Line
The RTEX-24’s specs point to a genuinely capable whole-home unit for small to mid-size households: 5.9 GPM max flow, 24kW of self-modulating power, a compact footprint, and adjustable temperature control. The tradeoff is a serious electrical requirement (three 40-amp breakers, 200-amp service recommended) that needs to be verified against your actual home setup before the rest of the spec sheet matters at all.
Frequently Asked Questions
What is the flow rate of the Rheem RTEX-24? Up to 5.9 GPM in warm climates, according to Rheem’s official specifications. Actual flow rate decreases as incoming groundwater temperature drops.
How many amps does the Rheem RTEX-24 need? It requires three 40-amp double-pole breakers, and Rheem recommends 200-amp household electrical service to support it.
What size are the Rheem RTEX-24 water connections? 3/4 inch NPT fittings at the bottom of the unit.
How much does the Rheem RTEX-24 weigh? 17.8 pounds, which is significantly lighter than a traditional storage tank water heater.
What temperature range does the Rheem RTEX-24 support? 80 to 140 degrees Fahrenheit, adjustable in 1-degree increments via the digital display.
How many heating elements does the Rheem RTEX-24 have? Three copper immersion heating elements, which allow the unit to self-modulate power based on demand.
What are the dimensions of the Rheem RTEX-24? 18.25 inches tall, 17.63 inches wide, and 3.5 inches deep.
Can the Rheem RTEX-24 run two showers at once? Yes, Rheem rates it for up to 2 showers and 2 sinks simultaneously in warm climates, based on its official specifications.
Does the Rheem RTEX-24 need special wiring? Yes. Real installations require substantial wire gauge (commonly 8-gauge copper for each of the three double-pole circuits) and sufficient conduit size to run them, which is a detail beyond the basic spec sheet.
Is the Rheem RTEX-24 the largest model in the RTEX lineup? Among the standard RTEX point-of-use and whole-home models, yes, it’s the largest at 24kW. Rheem does offer larger units like the 27kW and 36kW models under related product lines for bigger households.
References
- Rheem RTEX-24 official product specifications and full RTEX family comparison chart, via Amazon.com manufacturer content, accessed July 2026: https://www.amazon.com/dp/B01MS9DVEE
- Verified customer reviews describing installation, wiring, and heating element experiences, Amazon.com, accessed July 2026