Quick Answer: The best EcoSmart tankless water heater for most homes is the ECO 27 (27 kW) — a self-modulating whole-home electric unit rated 2.7 to 6.5 GPM depending on inlet temperature, usually around $500 street, with a limited lifetime warranty. Cold-climate whole-home buyers should step up to the 36 kW ECO 36 (3.6–8.7 GPM); warm-climate 1–2 bath homes save money and wiring with the 18 kW ECO 18 or 24 kW ECO 24; and single fixtures are covered by the ECO 11 (single 60A breaker) or the tiny POU 3.5 under a sink. Every GPM figure is a range on purpose — EcoSmart’s low number is your cold-winter reality, the high number is a warm climate.
EcoSmart is the value leader in electric tankless: copper-and-brass heating chambers, self-modulating power that draws only what the flow demands, field-replaceable elements, and a lifetime warranty on the whole-home line — usually at a lower price than Rheem or Stiebel Eltron. But EcoSmart’s model names are just kilowatts (ECO 8, 11, 18, 24, 27, 36), and the single most common buying mistake is reading the top of the published GPM range and ignoring the electrical service the unit demands. This guide ranks every current EcoSmart line for 2026 and shows you how to size one by amperage first, then climate.
EcoSmart’s model numbers, decoded
EcoSmart keeps naming refreshingly simple — but there are two things the model number doesn’t tell you:
- The number is the kilowatts, not the GPM. ECO 27 = 27 kW. Watts heat water; gallons-per-minute depend on how cold your incoming water is. That’s why every model lists a range (the ECO 27 is 2.7–6.5 GPM), not a single flow figure.
- Every kW step is also an amperage step. More kW means more breakers and more panel capacity. The ECO 11 lives on one 60A breaker; the ECO 36 wants roughly 150A of dedicated service. Your panel, not your bathroom count, is usually the real limit.
- Two product families share the “ECO” badge. The ECO 8–36 whole-home tankless units are the ones this guide ranks. The ECO MINI (2.5/4/6-gallon) models are mini-tanks, not tankless, and the POU line is small point-of-use tankless for a single sink. Don’t cross-shop them by kW.
Our top picks at a glance
| Model | Best for | Power | Flow range (inlet-dependent) | Electrical | Price |
|---|---|---|---|---|---|
| EcoSmart ECO 27 | Best overall value | 27 kW | 2.7–6.5 GPM | 3× 40A double-pole | ~$500 |
| EcoSmart ECO 36 | Best for cold climates | 36 kW | 3.6–8.7 GPM | 4× 40A (~150A service) | ~$680 |
| EcoSmart ECO 24 | Best warm-climate whole-home | 24 kW | 2.4–5.8 GPM | 3× 40A double-pole | ~$450 |
| EcoSmart ECO 18 | Best small home / apartment | 18 kW | 1.8–4.3 GPM | 2× 40A double-pole | ~$350 |
| EcoSmart ECO 11 | Best point-of-use / single breaker | 13 kW | 1.3–3.1 GPM | 1× 60A double-pole | ~$230 |
| EcoSmart POU 3.5 | Best under-sink | 3.5 kW | ~0.5 GPM (single fixture) | 120V/240V circuit | ~$130 |
By the numbers
- 2.7–6.5 GPM on the ECO 27 — the published range is entirely a function of inlet temperature; the low end is your cold-winter reality, the high end is a warm climate. — EcoSmart
- Limited lifetime warranty on the exchanger, electronics, and elements for the whole-home ECO 8–36 line (with registration and code-compliant install) — one of the strongest warranties in electric tankless. — EcoSmart
- ~150A of dedicated service (four 40A double-pole breakers) for the 36 kW ECO 36 — the reason many older 100–150A panels need an upgrade before the flagship. — EcoSmart
- Self-modulating design draws only the power the flow demands, with roughly 99% of the energy going into the water and no standby tank loss and no venting. — EcoSmart
- Electric tankless is about 24–34% more efficient than a standard storage tank for homes using up to ~41 gallons of hot water a day, per the U.S. Department of Energy — the efficiency case that makes a self-modulating EcoSmart pay back over time. — U.S. Department of Energy
1. EcoSmart ECO 27 — Best Overall Value
EcoSmart ECO 27 (27 kW Electric Tankless)
- The sweet spot in EcoSmart's lineup: enough kilowatts for a 1–2 bath home in most climates without stepping up to the 36's four-breaker electrical demand.
- Self-modulating heating with a digital thermostat adjustable in 1°F increments; copper-and-brass chamber with field-replaceable elements.
- Lifetime limited warranty on the exchanger, electronics, and elements when registered — rare at this price.
Get your tankless heater and fittings in two days — try Amazon Prime free for 30 days.
The ECO 27 is the EcoSmart we’d buy for most homes, and it’s the direct rival to the Rheem RTEX-24 at nearly the same ~$500 price. In warm and moderate climates its 2.7–6.5 GPM range covers two showers or a shower-plus-sink comfortably; in a northern winter it drops toward the low end, so read it as a solid one-to-two-fixture unit rather than a whole-house machine everywhere. The electrical bill of materials is the catch: three 40A double-pole breakers and heavy 8-gauge wire, which most 200A panels handle but many older services do not. Our best electric tankless roundup walks the full sizing ladder if you’re cross-shopping brands.
2. EcoSmart ECO 36 — Best for Cold Climates
EcoSmart ECO 36 (36 kW Electric Tankless)
- EcoSmart's flagship: the most kilowatts they make, and the only EcoSmart with a real shot at whole-home duty in cold climates.
- 3.6–8.7 GPM range; at a northern 40°F inlet, plan on roughly the bottom of that band — about two simultaneous fixtures.
- Needs roughly 150A of dedicated service (four 40A double-pole breakers), so a 200A panel and often a service review are part of the budget.
If you live where winter inlet water is genuinely cold and you’re set on electric, the ECO 36 is the EcoSmart to buy — nothing smaller has the power to hold temperature at a 60–70°F rise. But be honest about the electrical reality: 36 kW is roughly 150A of dedicated load, which often means a service upgrade on top of the heater. That’s the same math our electric vs gas comparison uses to steer large cold-climate homes toward gas — where a single gas condensing unit can push 9–11 GPM without touching your panel. For a two-bath home in a moderate climate, though, the ECO 36 is endless hot water with no venting and no gas line.
3. EcoSmart ECO 24 — Best Warm-Climate Whole-Home
EcoSmart ECO 24 (24 kW Electric Tankless)
- Same three-breaker electrical class as the ECO 27, a step down in kW and price — the value pick for warm and moderate climates.
- 2.4–5.8 GPM covers a 1–2 bath home where inlet water stays 60°F+; drops to one fixture in a hard winter.
- Self-modulating with the same lifetime limited warranty and field-replaceable elements as the rest of the whole-home line.
The ECO 24 is the quiet value play: it needs the same three 40A breakers as the ECO 27, so if your panel supports one it supports the other, and in a warm climate the ~$50 you save over the 27 buys essentially the same real-world experience. Choose the 24 if your inlet water rarely drops below 60°F and your peak demand is two fixtures; choose the 27 (or 36) if you want winter headroom. Either way, size by your coldest-month inlet, not the summer number.
4. EcoSmart ECO 18 — Best Small Home / Apartment
EcoSmart ECO 18 (18 kW Electric Tankless)
- Only two 40A breakers — the easiest whole-home EcoSmart to fit on a modest panel.
- 1.8–4.3 GPM handles a single-bath home, condo, or apartment in warm and moderate climates.
- Compact 17″ × 17″ × 3.5″ footprint mounts on a wall and reclaims the closet a tank used to fill.
For a one-bathroom home, apartment, condo, or ADU in a warm climate, the ECO 18 is the smart buy — two breakers instead of three, a lower price, and flow that’s plenty for a single shower plus a sink. Its 1.8–4.3 GPM range is the same climate lesson at a smaller scale: expect the top in Florida, the bottom in Minnesota. Where the inlet is cold or two showers run at once, step up to the ECO 24 or ECO 27 rather than fight the ceiling.
5. EcoSmart ECO 11 — Best Point-of-Use / Single Breaker
EcoSmart ECO 11 (13 kW Electric Tankless)
- Runs on a single 60A double-pole breaker — the easiest whole-house-style EcoSmart to retrofit into an existing panel.
- 1.3–3.1 GPM: a single shower or a warm-climate small apartment; endless hot water for the fixture it serves.
- Cheapest EcoSmart that still carries the whole-home lifetime limited warranty.
The ECO 11 is EcoSmart’s easy-install hero: one breaker, one heater, endless hot water at a bathroom, garage sink, cabin, or accessory unit. It’s a point-of-use unit first — pair it with the fixture it serves and it’s superb; ask it to run a northern two-bath house and it will disappoint. If a single 60A slot is all your panel can spare, this is the largest EcoSmart you can add without an upgrade.
6. EcoSmart POU 3.5 — Best Under-Sink
EcoSmart POU 3.5 (3.5 kW Point-of-Use Tankless)
- Tiny point-of-use tankless that mounts under a sink for instant warm water at a single tap — no long pipe run, no wait.
- Ideal for a powder room, bar sink, or utility sink far from the main water heater.
- Runs on a standard circuit (no heavy multi-breaker service), which makes it a true weekend DIY add.
When the problem is one remote sink that takes forever to run warm, you don’t need a whole-home unit — you need a POU 3.5 under the cabinet. At ~$130 and a standard circuit, it delivers warm water instantly to a single low-flow fixture. It won’t run a shower; it’s the surgical fix for a hand-wash sink, and it pairs neatly with a larger EcoSmart handling the rest of the house.
How to choose an EcoSmart tankless water heater
- Check your panel before your bathroom count. ECO 11 = one 60A breaker; ECO 18 = two 40A; ECO 24/27 = three 40A; ECO 36 = ~150A (four 40A). A panel upgrade often costs more than the heater — get an electrician’s load calc first.
- Size by your coldest-month inlet, not the box. Every ECO lists a GPM range; the low number is your winter reality. Look up your regional inlet temperature and size to the rise you actually need.
- Match the model family to the job. ECO 8–36 = whole-home/large-fixture; POU = single sink; ECO MINI = a mini-tank buffer, not tankless. Don’t compare them on kW alone.
- Register for the warranty. The lifetime limited coverage on whole-home ECO units requires registration and a code-compliant install — do both, and keep the electrician’s paperwork.
- Descale annually in hard water. EcoSmart’s copper-and-brass elements are field-replaceable, but scale still shortens life; add a scale filter and flush yearly.
The bottom line
For most homes, the EcoSmart ECO 27 is the best EcoSmart tankless water heater — a self-modulating 27 kW whole-home unit at ~$500 with a lifetime limited warranty and a realistic 2.7–6.5 GPM range. Cold-climate whole-home buyers should move up to the ECO 36, warm-climate and single-bath homes save real money with the ECO 24 or ECO 18, and single fixtures are covered by the one-breaker ECO 11 or the under-sink POU 3.5. EcoSmart’s whole game is matching kilowatts to your electrical service and your winter inlet temperature — get that right and it’s the best value in electric tankless. Comparing across brands? Start with our best electric tankless roundup, weigh it against the Rheem RTEX lineup, or read electric vs gas and tankless vs tank if you’re still choosing a fuel.