Rheem RTEX-24
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.
What owners report
Themes summarized from verified-purchase reviews across major retailers (4.5★ average, 2627 ratings). These are aggregated 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.
Price range from leading retailers
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