TL;DR
The “best” electric tankless water heater is the one that can actually hit your needed gallons per minute (GPM) at your home’s coldest incoming water temperature — and that your electrical service can support safely. For many homes, the decision comes down to whether you can power a 24–27 kW class unit without a panel/service upgrade, and whether you want a model that prioritizes temperature stability when demand spikes.
Top Recommended Electric Tankless Water Heaters
| Product | Best For | Price | Pros/Cons | Visit |
|---|---|---|---|---|
| Stiebel Eltron Tankless Water Heater – Tempra 24 Plus – | Whole-home priority on stable shower temps | $650 – $900 | Advanced flow control for steadier temps; may require 3 double-pole breakers and heavy wiring | Visit Amazon |
| EcoSmart ECOS 27 Tankless Electric Water Heater, 27 kW at | Value-focused higher-output whole-home installs | $450 – $500 | Compact, self-modulating design at a lower unit cost; some customer experience flags around replacement/wait times | Visit Amazon |
Top Pick: Best Overall Electric Tankless Water Heater
Stiebel Eltron Tankless Water Heater – Tempra 24 Plus –
Best for: A 1–2 bath home (or a 2-bath home with careful simultaneous-use expectations) where you want the shower to stay comfortable even when another fixture turns on — and you have (or are willing to add) the electrical capacity for multiple 240V circuits.
The Good
- Temperature stability focus: Stiebel Eltron’s Tempra Plus line is known for “Advanced Flow Control” (per the brand’s Tempra Plus product documentation), which can reduce flow to help hold your set temperature during spikes in demand.
- Solid whole-home orientation in the 24 kW class, which is often a practical “upper-mid” step before you get into even heavier electrical requirements.
- Strong installer-compatibility vibe in buyer reviews, with homeowners frequently emphasizing doing the electrical work the right way.
- A good fit for scenario planning: if you can live with the unit managing flow (instead of letting temperature sag), it tends to feel better in real showers.
The Bad
- Electrical reality check: many installs will require multiple dedicated 240V double-pole breakers (often three circuits) and appropriately sized copper conductors — not a casual DIY project.
- In cold-climate winters (very low incoming water temps), a 24 kW unit may not deliver “whole-home” hot water at high GPM without tradeoffs; flow control can mean reduced flow at fixtures.
- Like any electric tankless, scale can hurt performance in hard-water areas unless you plan for isolation valves and periodic descaling.
4.6/5 across 669 Amazon reviews
“Installed June 2022INSTALL NOTE – I am not a plumber and this stretched my mechanical DIY-er mentality, but I did install this on my own: be careful if you choose to install this on your own. I chose NOT to do the electrical upgrade required on my own – the risk of not getting that right was too high, so I paid my electrical contractor to upgrade the box…” — Verified Amazon buyer (5 stars)
“Amazon ReviewProduct: Stebo Electron Tankless Water Heater Temperature 24+ Electric On-Demand Water HeaterRating: 3 out of 5 starsHeadline: Simple but expensive to installReview:The Stebo Electron tankless water heater is a simple and sleek design that heats water on demand, saving energy and space. However, it is important to note that installation can be…” — Verified Amazon buyer (4 stars)
“I chose NOT to do the electrical upgrade required on my own – the risk of not getting that right was too high, so I paid my electrical contractor to upgrade the box for the 3 x 50 amp breakers – NO REGRETS!” — verified buyer, 5 stars
Our Take: If you want a whole-home electric tankless that puts temperature stability first (especially for showers) and you can support the multi-circuit electrical demand with a licensed electrician working to NEC requirements, the Tempra 24 Plus is the most confidence-inspiring pick in this shortlist.
EcoSmart ECOS 27 Tankless Electric Water Heater, 27 kW at
Best for: A homeowner doing a higher-output retrofit in a garage or utility room who wants a more budget-friendly unit price — and has enough panel capacity and breaker spaces to support a high-kW tankless on dedicated circuits.
The Good
- Higher power class (27 kW) can help in shoulder-season and cooler incoming-water conditions, where smaller units run out of heating headroom faster.
- Self-modulating operation (per manufacturer positioning) is appealing for homeowners trying to avoid wasting energy when demand is low.
- Compact, light wall-mount form factor can make physical placement easier than a bulky tank, especially during replacements.
- Lower upfront unit price compared to some premium whole-home electric tankless lines.
The Bad
- Buyer reviews indicate lower review volume versus long-established models, which gives you less “crowd data” to rely on.
- Some customer experience notes mention replacement/waiting frustrations — a risk if this unit is your only hot-water source.
- Electrical needs are still substantial at 27 kW; if your service/panel is marginal, install costs can dwarf the purchase price.
4.1/5 across 13 Amazon reviews
“Bought this to replace my old water heater that went bad. Though this unit was narrower than the old one and did not fit the wall stud spacing, it is light enough that sheet rock anchors are sufficient to hold it. My only concern was the plastic water fittings. Only time will tell if they hold up sufficiently. Wiring was simple enough. Operation is simple.…” — Verified Amazon buyer (5 stars)
“do not buy broken after six weeks waiting over week for replacement still waiting husband just died now no hot water;last one same brand lasted nine yerars” — Verified Amazon buyer (1 stars)
Typical price: $450 – $500
Our Take: If your main goal is more electric tankless output per dollar and you’re already prepared for the wiring and breaker requirements, the ECOS 27 is a compelling value-oriented option — just go in with eyes open about support/replacement friction noted in customer experience.
FAQ
How do I size an electric tankless water heater for my home?
Start with temperature rise: subtract your coldest incoming water temperature (winter groundwater temp, not summer) from your desired outlet temperature. Then estimate peak simultaneous flow (GPM) by adding the fixtures you’ll realistically run at once (for example, a shower plus a sink). The U.S. Department of Energy explains the core limitation clearly: tankless units are constrained by flow rate, and performance depends on the temperature rise you’re asking the heater to deliver (see the U.S. Department of Energy tankless water heater overview).
Will a whole-home electric tankless water heater work in cold climates?
It can, but “whole-home” gets harder as incoming water gets colder, because the heater has to add more heat to each gallon. In cold climates, many households either step up to higher kW models (with heavier electrical requirements) or use multiple smaller point-of-use heaters to cover the most important fixtures without pushing one central unit past its comfort zone.
How many breakers does an electric tankless water heater need?
Many whole-home electric tankless units require multiple dedicated 240V double-pole breakers (commonly 2–3 circuits), plus appropriately sized conductors and terminations. This is why we recommend confirming your panel capacity, spare breaker spaces, and service size before you buy — and having a licensed electrician size and install everything to the NFPA’s National Electrical Code (NEC) and your local amendments.
Why does electric tankless water heater temperature fluctuate in the shower?
Two common causes are (1) demand spikes (someone opens another hot tap) and (2) flow rates dropping too low for stable regulation. Some designs include flow control that intentionally reduces flow to hold the set temperature instead of letting outlet water go lukewarm. Stiebel Eltron describes this approach in its Tempra Plus materials (see Stiebel Eltron’s Tempra Plus overview).
Do I need a panel upgrade for an electric tankless water heater?
Sometimes, yes — and it’s often the biggest cost driver. If your service is 100A (or a tight 150A) and you’re adding a 24–27 kW tankless that wants multiple high-amperage circuits, you may run out of capacity quickly once you add up other large loads (range, dryer, HVAC, EV charging). A licensed electrician can do a load calculation and tell you whether you’re looking at a straightforward circuit add, a subpanel, or a full service upgrade.
How often should I descale an electric tankless water heater?
It depends on water hardness and usage. In hard-water areas, scale buildup can reduce performance and trigger errors, so many homeowners plan on periodic flushing/descaling as routine maintenance. If you’re installing a whole-home unit, consider isolation valves for easier flushing and talk with a plumber about whether a scale filter or water softener makes sense for your specific water quality.
Is it smarter to install one whole-home unit or multiple point-of-use heaters?
Multiple point-of-use electric tankless heaters can be a practical strategy when (a) your incoming water is cold, (b) your panel can’t support a large single unit, or (c) only a couple fixtures really need strong hot water at the same time. A whole-home unit is simpler from a “one device does it all” perspective, but it concentrates electrical demand in one place and often increases the odds of a costly electrical upgrade.
Bottom Line
If you want the best chance at comfortable, stable hot water from a whole-home electric tankless — especially in real-life scenarios like “someone starts the dishwasher while you’re mid-shower” — the Stiebel Eltron Tempra 24 Plus is our top pick from this shortlist. Just treat the electrical requirements and hard-water maintenance plan as part of the purchase, not optional extras.
Affiliate disclosure: We may earn affiliate commissions from qualifying purchases. This doesn't influence our reviews.
