Quick Answer: The best electric tankless water heater for most homes is the Stiebel Eltron Tempra 36 Plus — a 36 kW unit rated up to ~7 GPM whose Advanced Flow Control quietly reduces flow to keep water at your set temperature instead of going cold. The Rheem RTEX-36 is the pick for the largest homes and colder climates, while the EcoSmart ECO 27 is the best value at under $600. All of these need serious 240V service — confirm your panel before buying. Flow ratings assume a warm inlet; cold winter water lowers real GPM.
Last updated August 7, 2026: re-verified all five prices against current Home Depot and manufacturer-dealer listings — no changes (EcoSmart ECO 27 ~$574, Rheem RTEX-36 ~$655, Stiebel Eltron Tempra 36 Plus ~$733-$850 depending on retailer). Previous update (July 2026) added a whole-home 240V vs point-of-use 120V comparison table, because the two are separated by roughly a factor of ten in power and are routinely cross-shopped by mistake.
Electric tankless water heaters are compact, need no venting, and run about 98–99% efficient at the unit, which makes them ideal where there’s no gas line or for a warm-climate home. The catch is electrical demand: whole-home units pull enormous amperage, and their usable GPM drops as incoming water gets colder. We ranked the best 240V units on power (kW), warm-climate flow (GPM), controls, and the electrical service they realistically require.
Our top picks at a glance
| Model | Best for | Power | Max Flow | Efficiency | Price |
|---|---|---|---|---|---|
| Stiebel Eltron Tempra 36 Plus | Best overall | 36 kW | ~7 GPM | ~99% | ~$850 |
| Rheem RTEX-36 | Largest homes / cold climates | 36 kW | ~8 GPM | 99.8% | ~$650 |
| EcoSmart ECO 27 | Best value | 27 kW | ~6.6 GPM | ~0.94 UEF | ~$570 |
| Rheem RTEX-24 | Moderate 2-bath home | 24 kW | ~4.7 GPM | 99.8% | ~$600 |
| Stiebel Eltron Tempra 24 Plus | Warm-climate 2-bath | 24 kW | ~4.7 GPM | ~99% | ~$700 |
By the numbers
- ~98–99% energy efficiency at the unit for electric tankless — nearly all the electricity becomes hot water, since there’s no flue loss. — U.S. Department of Energy
- ~150 amps of 240V service needed for a 36 kW whole-home unit (three 40A double-pole breakers), which is why a panel check is non-negotiable before buying. — manufacturer install specs (Stiebel Eltron / Rheem)
- ~$44 saved per year on average by switching from an electric tank to an electric tankless for a typical household — the savings are smaller than gas because electric tanks are already efficient. — ENERGY STAR
1. Stiebel Eltron Tempra 36 Plus — Best Overall
Stiebel Eltron Tempra 36 Plus
- 36 kW delivers up to ~7 GPM in warm and moderate climates — enough for a whole home in much of the country.
- Advanced Flow Control gently throttles flow to hold your set temperature instead of dropping to lukewarm under heavy demand.
- Digital temperature display, quiet operation, and a strong reliability reputation.
- Needs roughly 150A of 240V service across multiple breakers — plan the electrical work.
The Tempra 36 Plus is the electric unit we’d put in most homes without a gas line. Its Advanced Flow Control is what separates it from cheaper units: when two showers and the dishwasher all run at once, it slightly reduces flow rather than letting the temperature collapse — the difference between “still hot” and “why is it cold.” It’s premium-priced for an electric unit, but it earns it — and if you like the brand, our full Stiebel Eltron lineup guide ranks the smaller, cheaper Tempra 24, 20, and 15 Plus too. If you have a gas line, compare against our best overall picks first.
2. Rheem RTEX-36 — Best for Largest Homes & Cold Climates
Rheem RTEX-36 Electric Tankless
- 36 kW self-modulating unit rated up to ~8 GPM in warm climates — the most flow of any unit here.
- 99.8% efficient with external digital thermostatic control in 1°F increments.
- The one to size up to when your incoming water runs cold in winter.
Because electric flow falls as inlet water gets colder, Northern buyers should default to the biggest unit they can power. The Rheem RTEX-36 pairs 36 kW with self-modulating power and costs less than the Stiebel — the trade-off is it lacks the Tempra’s flow-throttling smarts, so correct sizing matters even more. It needs the same heavy electrical service. Rheem’s electric range runs from 13 to 36 kW across two differently-named catalogs (RTEX pro vs RETEX retail) — our Rheem tankless lineup guide decodes the whole ladder.
3. EcoSmart ECO 27 — Best Value
EcoSmart ECO 27 Electric Tankless
- 27 kW self-modulating unit rated up to ~6.6 GPM, with a low 0.3 GPM activation flow.
- Compact wall mount with digital temperature control.
- Lifetime limited warranty — conditions apply (annual maintenance, pro install, softener on hard water).
For a warm-climate 2- to 3-bath home, the EcoSmart ECO 27 is the best value in electric tankless. At under $600 it covers real whole-home demand where the inlet water is mild. Read the warranty fine print — the “lifetime” coverage requires annual maintenance and a water softener on hard water — but for a sunbelt home it’s a lot of heater for the money. EcoSmart’s smaller ECO 18 (about $425) and ECO 11 (about $208) suit apartments and point-of-use — see our full EcoSmart tankless lineup guide for the whole ECO 8–36 sizing ladder, or our dedicated best tankless water heater for apartment guide if you’re renting or working with a multi-family electrical panel.
4. Rheem RTEX-24 — Best for a Moderate 2-Bath Home
Rheem RTEX-24 Electric Tankless
- 24 kW self-modulating unit; rated ~4.68 GPM (Home Depot) to ~5.9 GPM in warm climates.
- Needs about 100A of dedicated 240V service — lighter than the 36 kW units.
- Digital external control and a compact footprint.
If your panel can’t support a 150A tankless load, the 24 kW RTEX-24 is the practical whole-home step down for a moderate 2-bath home in a warm or mild climate. Note the flow spread you’ll see quoted — Rheem lists ~5.9 GPM “warm climate” while Home Depot shows 4.68 GPM — a good reminder that GPM is climate-dependent, not a fixed number.
5. Stiebel Eltron Tempra 24 Plus — Best Warm-Climate 2-Bath
Stiebel Eltron Tempra 24 Plus
- 24 kW with the same Advanced Flow Control as the flagship, sized for milder inlet water.
- Premium controls and quiet, reliable operation.
- A great fit for a Sunbelt 2-bath home that wants the Stiebel experience for less.
The Tempra 24 Plus brings Stiebel’s flow-throttling control to a 24 kW body. In a warm climate where you don’t need 36 kW, it’s the refined pick — you get the “always hot” behavior without paying for the flagship’s power or the electrical service it demands.
Whole-home 240V vs point-of-use 120V: don’t cross-shop them
The picks above are all 240-volt whole-home heaters. A large share of electric-tankless searches actually want a 120-volt point-of-use unit for one sink, and the two are separated by a factor of ten in power. This table is the fastest way to tell which one you are shopping for.
| Whole-home 240V | Point-of-use 120V tankless | Point-of-use mini-tank | |
|---|---|---|---|
| Typical power | 18–36 kW | 3.0–3.5 kW | 1,440 W |
| Continuous flow at a 60°F rise | ~1.5–4.0 GPM | ~0.40 GPM | ~0.16 GPM (plus 2.5–7 stored gallons) |
| Runs a shower? | Yes | No | No |
| Electrical service | Up to ~150A, multiple double-pole breakers | Dedicated 25–30A breaker | Standard 120V outlet |
| Example | Stiebel Eltron Tempra 36 Plus | Rheem RETEX-04T (0.68 GPM rated) | Bosch Tronic 3000T ES2.5 |
| Typical price | $450–900 | $189–219 | $150–290 |
The arithmetic behind those flow figures is the same one manufacturers use: BTU/hr = GPM × 500 × temperature rise. A 3.5 kW unit produces 11,942 BTU/hr, which is why Home Depot’s listing for the Rheem RETEX-04T rates it at just 0.68 GPM — and that rating already assumes a modest ~35°F rise. If your job is a single remote sink, read our best point-of-use water heater guide instead of buying a whole-home unit you can’t power.
How to choose an electric tankless water heater
- Match kW to your climate: Colder inlet water needs more kW for the same GPM. Warm climate → 24 kW can do a 2-bath; cold climate → step up to 36 kW.
- Confirm your panel first: A 36 kW unit can draw ~150A. Many homes need a 200A service and multiple dedicated double-pole breakers — see our tankless water heater electrical requirements guide for the exact breaker count and wire gauge by model before you buy.
- Size for peak flow: Add up fixtures you’ll run at once (a shower is ~2–2.5 GPM). Undersizing causes lukewarm water; it’s the most common complaint.
- Look for flow control: Units like the Stiebel Tempra that throttle flow keep temperature steady under load — a real-world advantage over simple on/off units.
- Read the warranty conditions: “Lifetime” warranties often require annual maintenance and a softener on hard water.
- Want near-silent operation? Electric units skip the combustion fan and burner that give gas tankless its characteristic hum — see our tankless water heater noise guide for real dB figures on both.
The bottom line
The Stiebel Eltron Tempra 36 Plus is the best electric tankless water heater for most homes: enough power for whole-home use and Advanced Flow Control that keeps water hot under load. In a cold climate or a big house, the Rheem RTEX-36 gives you the most flow for less money. Watching your budget in a warm climate? The EcoSmart ECO 27 is a lot of heater for under $600. Whichever you choose, confirm your electrical service first — and if you have a gas line, weigh the electric vs gas trade-offs before deciding. For a side-by-side pick by bathroom count across both fuel types, see our best whole-house tankless water heater guide. One brand you won’t find above: Bosch. Its Tronic 3000 electric line tops out at 12 kW, a point-of-use ceiling well short of whole-home capacity — see our best Bosch tankless water heater guide for why that rules it out here. A budget-tier alternative worth knowing about: the Marey ECO270 (220V, 27 kW, 6.5 GPM) undercuts the Stiebel and Rheem on price for warm-climate whole-house use — see our best Marey tankless water heater guide for the full lineup including its point-of-use models. Another budget-tier option sold at Home Depot and Ace Hardware rather than through HVAC contractors: Titan’s N-120/N-160/N-210 lineup, which trades WiFi and app control for a lower unit price — see our best Titan tankless water heater guide for which model fits your panel. Rheem also sells its own budget-tier line: the Home Depot-focused Richmond RMTEX-27 undercuts a comparable RTEX-class Rheem on price — see our best Richmond tankless water heater guide for the details.