Rheem RTEX-24
Amazon customer rating as of
Tankless Geek editorial score: 4.4/5
The Rheem RTEX-24 is a 24 kW, 240-volt electric tankless water heater aimed at whole-home use — Rheem's Professional Classic point where electric tankless becomes viable for more than a single fixture. It self-modulates power to the incoming flow, holds temperature to within about ±1 °F, and is set through a digital display with 1-degree increments from 80 to 140 °F.
Electric tankless heaters live and die by two numbers: kilowatts and incoming water temperature. At 24 kW the RTEX-24 is rated up to 5.9 GPM, but that peak only holds at a very small temperature rise; in cold-groundwater regions usable flow falls to roughly 2–3 GPM. It's compact (about 18 lb, under 4 inches deep) and clean to install on the plumbing side — the catch is electrical. It needs three 40-amp double-pole breakers (roughly 120 A of service) and 8-gauge wiring, which is a real panel consideration for many homes.
Key Features
Best Use Cases
Our Verdict
The RTEX-24 is one of the better-value whole-home electric tankless units, and thousands of owner reviews back that up: endless hot water, easy plumbing install, and precise digital temperature control. Judge it honestly on climate and electrical capacity, though. Its 5.9 GPM headline is a warm-water-in figure — in a cold climate you should plan for two fixtures at most, often one. And the electrical demand is significant: three 40 A breakers and 8-gauge wire mean many older homes need a panel upgrade, which can dwarf the unit's price. Our take: a strong pick for warm-climate homes or as an electric whole-home unit where gas isn't available — but confirm your panel can feed it, and size your flow expectations to your incoming water temperature, not the box.
Technical Specifications
| Power | 24 kW · 240 V |
|---|---|
| Max flow rate | 5.9 GPM (at minimal temperature rise) |
| Minimum flow | 0.3 GPM |
| Efficiency | 99.8% (electric) |
| Temperature control | 80–140 °F, digital, ±1 °F, 1° increments |
| Electrical requirement | Three 40 A double-pole breakers (~120 A) |
| Wiring | 8-gauge (three runs) |
| Dimensions (W×H×D) | 17.6 × 18.25 × 3.5 in |
| Weight | 18 lb |
| Modulation | Self-modulating power output |
| Warranty | 5 yr heating chamber · 1 yr parts |
Specifications verified against the linked source documents. See Sources below.
How much hot water you'll actually get
Usable flow drops as incoming water gets colder. Figures are calculated from rated output (kW) and labeled as such — not bench-tested by us.
| Temperature rise | Typical scenario | Usable flow |
|---|---|---|
| 35 °F | Warm climate (75 °F in → 110 °F) | 4.7 GPM |
| 45 °F | Mild climate (65 °F in → 110 °F) | 3.6 GPM |
| 60 °F | Cool climate (50 °F in → 110 °F) | 2.7 GPM |
| 70 °F | Cold climate (40 °F in → 110 °F) | 2.3 GPM |
Usable flow calculated from electric output (24 kW × 3,412 BTU ÷ (ΔF × 500)). The 5.9 GPM maximum is only reached at a very small (~28 °F) rise; realistic flow tracks the table below.
Pros
Cons
Buy it if…
- Homes without gas that want whole-home electric hot water
- Warm-climate regions where incoming water is above ~60 °F
- Owners with (or willing to add) 120 A of panel capacity and 8-gauge wiring
- Anyone wanting precise digital temperature control in 1° steps
Skip it if…
- Cold-groundwater regions with high simultaneous demand — flow drops sharply
- Older homes with limited electrical panel capacity
- Buyers who'd get cheaper hot water from a gas tankless where gas is available
- Large households routinely running 3+ fixtures at once
Installation Requirements
Professional vs DIY
The three-circuit/~120 A electrical work calls for an electrician and a permit; the plumbing side is simple.
Gas and electrical work should be done by a licensed professional, and most installs require a permit and must meet local building codes — DIY work can void the manufacturer warranty. Always confirm the unit's own manual for exact clearances, venting, and sizing.
What owners report
Themes summarized from retailer customer feedback (4.5/5 Amazon customer rating, 2627 ratings, as of 2026-08-23). These are owner opinions, not our own bench testing.
With thousands of reviews, owners consistently report endless hot water and a straightforward plumbing-side install for an electric unit.
Precise, stable digital temperature control (±1 °F) and a compact, light chassis that mounts almost anywhere.
The electrical requirement is the recurring theme — three 40 A breakers and 8-gauge wire mean many homes need a panel upgrade before install.
The 5.9 GPM rating isn't achievable in cold climates; owners in colder regions note usable flow drops to roughly 2–3 GPM.
A minority report element or unit failures, most often traced back to undersized or marginal electrical supply.
Rheem RTEX-24 FAQ
What electrical service does the RTEX-24 need?+
It draws 24 kW at 240 V — about 100 A of current — wired as three 40-amp double-pole breakers with 8-gauge wire. Many homes, especially older ones, need a panel upgrade to supply this. Factor that cost in before buying; it can exceed the price of the heater itself.
Can it really do 5.9 GPM?+
Only at a very small temperature rise (warm incoming water). Electric output is fixed at 24 kW, so as incoming water gets colder, flow must drop to keep the set temperature. In a cold climate, plan for roughly 2–3 GPM — one to two fixtures — not the headline 5.9.
Is it a true whole-house unit?+
In warm climates, yes, for a small-to-medium home. In cold-groundwater regions it's better thought of as a one-to-two-fixture unit. Match it to your incoming water temperature, not just the GPM on the box.
How accurate is the temperature?+
It holds the setpoint to about ±1 °F and is adjustable in 1-degree steps from 80 to 140 °F via the digital display — one of the reasons owners like it for consistent shower temperatures.
What's the warranty?+
5 years on the heating chamber and 1 year on parts — typical for a residential electric tankless, and shorter than gas heat-exchanger coverage.
Product sources
Specifications verified 2026-08-23. Manufacturer documents are treated as the primary source for model specifications. Retailer pages are used only for customer ratings and owner-feedback themes.
- Rheem — Professional Classic Tankless Electric RTEX-24 (accessed 2026-08-23)
- Rheem RTEX-24 specifications (Water Heater Manuals) (accessed 2026-08-23)
- Amazon — Rheem RTEX-24 listing (rating & buyer reviews) (accessed 2026-08-23)
Price range from leading retailers
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