Exploring
The EcoSmart ECO 18 is the best tankless water heater for most homes — whole-house electric capacity with patented self-modulating control. The Stiebel Eltron Tempra 29 Plus is the premium German-engineered pick, and the EcoSmart ECO 8 covers point-of-use and small-cabin duty.
How We Picked
We compared flow rate (GPM), self-modulating temperature control, electrical requirements, and owner reliability reports across electric tankless water heaters. Electric units are the right fit where grid or generator power is available; for fully off-grid propane hot water, see our propane tankless water heater comparison and camping shower guide. Pair any whole-house unit with clean water from our whole-house filter picks.
1. Best Overall: EcoSmart ECO 18 Electric Tankless Water Heater
EcoSmart ECO 18 Electric Tankless Water Heater
EcoSmart
- 18 kW at 240V — whole-house capacity for most climates
- Patented self-modulating technology only draws what you use
- Up to 4.3 GPM — two showers at once in warm regions
- Digital thermostat in 1° increments
- 4.3★ from 2,400+ owners
Why we picked it: The ECO 18 hits the sweet spot of the whole EcoSmart line: enough output to run a shower and a sink together in most of the country, self-modulating power draw that keeps electric bills in check, and a compact wall-mount footprint that frees up the closet a tank heater used to fill. Owners in mild and moderate climates report it comfortably handles a small home — the reason it's our best overall tankless water heater.
2. Best Premium: Stiebel Eltron Tempra 29 Plus
Stiebel Eltron Tempra 29 Plus
Stiebel Eltron
- 28.8 kW — true whole-house output even in cold climates
- Advanced Flow Control keeps temperature rock-steady
- German-made with decades of tankless engineering
- Silent operation, no venting required
- 4.4★ owner rating
Why we picked it: Stiebel Eltron has built tankless heaters longer than almost anyone, and the Tempra 29 Plus shows it: its Advanced Flow Control quietly trims flow instead of letting the water run cold when demand spikes — the failure mode cheaper units are known for. With nearly 29 kW on tap it delivers hot showers even from near-freezing groundwater. If you want the electric tankless water heater that feels like infrastructure, this is it.
3. Best Point-of-Use: EcoSmart ECO 8 Tankless Water Heater
EcoSmart ECO 8 Tankless Water Heater
EcoSmart
- Compact 8 kW unit for single fixtures or small cabins
- Same self-modulating control as the big EcoSmarts
- Roughly the size of a shoebox — mounts anywhere
- Ideal for a sink, shower, or workshop washbasin
- 4.2★ from 700+ owners
Why we picked it: Not every building needs whole-house capacity. The ECO 8 brings on-demand hot water to a guest cabin, workshop sink, or single bathroom for a fraction of the cost and electrical load of its big siblings — and its shoebox footprint mounts under a sink or inside a vanity. For point-of-use hot water on a homestead, it's the simplest answer we've found.
Comparison Table
| Pick | Heater | Output | Flow | Best for |
|---|---|---|---|---|
| Best Overall | EcoSmart ECO 18 | 18 kW | Up to 4.3 GPM | Most homes & homesteads |
| Best Premium | Stiebel Eltron Tempra 29 Plus | 28.8 kW | Whole-house | Cold climates, larger homes |
| Best Point-of-Use | EcoSmart ECO 8 | 8 kW | Single fixture | Cabins, workshops, one bath |
What to Look For in a Tankless Water Heater
Electric vs. propane. An electric tankless water heater is simpler — no venting, no fuel lines, near-silent — but demands serious amperage (the ECO 18 wants two 40A breakers; the Tempra 29 Plus three). A propane tankless water heater trades breaker panels for a fuel line and vent, and is the practical choice where grid power is limited — that's a separate buying decision we cover in our propane tankless comparison.
Flow rate and temperature rise. Size by the coldest water you'll ever feed it. A unit that delivers 4+ GPM from 60°F groundwater may manage barely 2 GPM from 40°F winter well water. Add up the fixtures you actually run simultaneously — shower (2 GPM) plus kitchen sink (1.5 GPM) — and match that at your winter inlet temperature.
Self-modulating control. The feature that separates the picks above from bargain units: the heater continuously adjusts its element power to the flow passing through, so a trickle doesn't scald and a full shower doesn't run lukewarm — and you only pay for the electricity each draw actually needs.
Electrical requirements. Check your panel before you buy. Whole-house electric tankless units routinely require 150+ amps of dedicated breaker capacity at 240V. The point-of-use ECO 8 needs a single 40A double-pole breaker — one reason small units make so much sense for outbuildings.
Bottom Line: Which Should You Buy?
For most homes: the EcoSmart ECO 18. Whole-house on-demand hot water with self-modulating efficiency.
For cold climates: the Stiebel Eltron Tempra 29 Plus. The German-engineered flagship that never runs cold.
For one fixture or a cabin: the EcoSmart ECO 8. Point-of-use hot water the size of a shoebox.
Ready to buy?
Jump straight to our top picks on Amazon — prices shown at click-through.
Frequently Asked Questions
How does a tankless water heater work?
Instead of keeping 40–50 gallons hot around the clock, a tankless water heater runs cold water past high-power heating elements (or a gas burner) the instant a tap opens, heating it on the way to the fixture. Close the tap and it shuts off — which is why tankless units are also called on-demand water heaters and why they never "run out" of hot water.
What are the pros and cons of a tankless water heater?
Pros: endless hot water, 10–30% lower water-heating energy use, a 20+ year service life, and a wall-mount footprint. Cons: higher upfront cost, big electrical or gas-line requirements, and flow limits — an undersized unit runs lukewarm when two showers compete. Sizing to your winter groundwater temperature avoids nearly every complaint.
Can I run an electric tankless water heater off-grid?
Realistically, no — whole-house electric units draw 75–120+ amps at 240V, beyond what most inverter and battery systems deliver continuously. Off-grid, the standard answer is a propane tankless water heater; see our propane tankless comparison for the two we recommend. Electric tankless shines on grid or generator-backed homesteads.
What size tankless water heater do I need?
Add the flow of fixtures you run at once (shower ~2 GPM, sink ~1.5 GPM), then check the unit's output at your winter inlet temperature. Warm regions do fine with 18 kW for a small home; cold-climate whole-house duty wants 27–29 kW. A single bathroom or cabin sink is happy with an 8 kW point-of-use unit.
Do tankless water heaters work for RVs?
Yes, but RV tankless water heaters are almost always propane-fired, compact units sized for a rig's plumbing — a different animal from the residential electric units in this guide. If your hot-water plans are mobile, the portable propane units in our camping shower guide are the better starting point.
Related Guides
How We Research
Picks are based on manufacturer specifications, current Amazon availability, and patterns across verified owner reviews. Flow rates vary with inlet water temperature — confirm output at your winter groundwater temperature before buying.
Installation note: Whole-house electric tankless heaters require dedicated 240V circuits sized well beyond a typical tank heater — a licensed electrician should confirm panel capacity and pull permits. Never undersize wire or breakers for a high-amperage appliance.