The Best Electric Tankless Water Heaters of 2026

The electrical requirement is the reason this one wins. It needs three dedicated 40-amp breakers with 8-gauge copper and a minimum of 200-amp service to the house. Plenty of homes built in the last few decades already have 200-amp service, so you may need an electrician and a few breakers rather than a whole new meter base. The 36 kW units in this guide ask for far more. That gap often decides whether this project costs hundreds or thousands.

Temperature stability is the complaint that sinks cheap electric tankless heaters. You turn on the kitchen tap mid-shower and the shower goes lukewarm. Stiebel Eltron's flow control is built to hold output temperature by trimming flow instead of letting the water run cooler, and the brand's reputation among installers rests on exactly that behavior. You also get two temperature memory presets, so switching between a dish-washing temperature and a shower temperature takes one button.

It's a 19-pound box, about 14.5 by 16.6 inches and under 5 inches deep, with no venting. That means you can hang it in a utility closet, a laundry nook or the spot where your old tank used to squat and get the floor space back. If you've been eyeing that closet for a washer-dryer stack or shelving, this is the part of the upgrade you'll notice every week.

On output, be realistic. At 28.8 kW you've got roughly enough power for one shower plus a sink in cold-groundwater regions, and comfortably more than that where incoming water sits near 70°F. The DOE pegs demand-type heaters as 24% to 34% more efficient than tank models in homes using 41 gallons a day or less, and electric resistance tankless units rate around 0.98 to 0.99 UEF. You're not losing energy here. You're just limited by watts.

Flaws but not dealbreakers

It costs considerably more than the EcoSmart and Rheem whole-house units, and the installation isn't cheap either. Three 40-amp circuits mean real copper, real conduit and usually a permit. If your panel is full, add a subpanel to the budget.

Wire it at 208 volts instead of 240 and the maximum draw drops to 21,600 watts, which is a meaningful cut in capacity. That matters in some condos and commercial buildings. Check your actual service voltage before you order.

Owner feedback on Stiebel's larger Tempra units repeatedly circles back to the same lesson: people underestimate the electrical scope. The heater is the easy part.

If you're heating one bathroom, this is the unit to look at first. At 13 kW and 54 amps it needs one circuit, not three, which keeps the electrical work inside what a typical panel can absorb. The listing rates it up to 3.17 GPM — that's a warm-climate number, and you should expect roughly half that where winter groundwater runs cold. For a single shower or a shower plus a low-flow faucet, it's usually enough.

The digital thermostat is the feature that makes it livable. You adjust in one-degree steps on an external display, so dialing in a temperature that's hot enough to clean dishes but not hot enough to scald takes a minute. Self-modulating power control means it only pulls the wattage the current flow needs, instead of running flat out and overshooting. That's the behavior you want when someone flushes mid-shower.

It's a 4-pound box roughly 12.6 by 8.25 inches and under 4 inches deep, with half-inch NPT adapters included and side compression connections. Owners regularly describe straightforward installs in cabins, tiny houses and apartments. The copper immersion elements are threaded and field-serviceable, so a scaled element is a part swap rather than a new heater.

This is also the most widely owned unit in our lineup by a wide margin, which means the failure patterns are well documented. The recurring theme in owner feedback is that hard water shortens element life — a few owners report needing service around the three-year mark. Flush it, or soften your water, and that story changes.

Flaws but not dealbreakers

Thirteen kilowatts is one bathroom's worth of power. You can't run two showers, and in a cold climate you can't reliably run a shower and the kitchen sink at once. Owners in cold-weather cabins say exactly that.

Scale is the known weak point. Several owners describe elements failing after a few years on hard water, and the fix is periodic descaling that many people never do.

Read the one spec that matters here: it's configured for incoming water around 60°F. That's not marketing hedging, it's the sizing assumption. In Florida, Texas, Arizona or coastal California, that's your reality most of the year and this unit does fine for a bathroom. In Michigan in January, incoming water can be 40°F and this heater will struggle. Buy it for the climate it's built for.

Self-modulating control means it ramps power up and down with flow, so a trickle at the bathroom sink doesn't trigger full wattage. For a condo or a small rental where demand is one person at a time, that's the right design. It's also only 6.5 pounds and about 13.5 by 10 inches, so it mounts almost anywhere you can find a stud and a water line.

Compared with the Rheem RTEX-13 at the same 13 kW, the practical difference is control and documentation. Rheem gives you a one-degree external display and published amperage; EcoSmart's listing is thinner on detail. If you want to know exactly what breaker you're buying before the box arrives, the Rheem tells you more.

Flaws but not dealbreakers

The listing is unusually sparse — no stated amperage, no GPM chart, no temperature-rise table. For a device that needs a dedicated high-amperage circuit, that's a real inconvenience; you'll want the manufacturer's install manual before you call an electrician.

It's a one-fixture-at-a-time heater, and in cold-groundwater regions it's a marginal one. Don't buy it hoping to cover a whole house.

This is the unit for a big house with real simultaneous demand — several bathrooms running at once, a cold climate, or both. At 36 kW it has the headroom that 27 and 28.8 kW units don't. Owners with upgraded service describe running three hot showers at the same time without the temperature sagging. If that's your actual problem, nothing smaller in this guide solves it.

The catch is written right on the listing: it draws 150 amps and needs a minimum of 300-amp service. Most houses have 100 or 200. Upgrading service means the utility, the meter base, a new panel and a permit, and it routinely costs more than the heater. Several owners say plainly that they had to upgrade their service first and that the install outran the unit's price. Price the electrical work before you price the heater.

The hardware itself is simple: digital temperature control, no venting, a 19-pound wall box. Stiebel Eltron's materials claim you'll save at least 15% to 20% on the hot-water portion of your electric bill versus a tank, and the efficiency numbers back the direction of that claim — electric resistance tankless units rate around 0.98 to 0.99 UEF, with no standby loss. Whether it pencils out depends entirely on your utility rate.

One quirk worth knowing: if the power light on the front cover blinks, the unit is telling you it can't heat the flow you're asking for, and the fix is to reduce flow. That's useful feedback, but it also means the heater has a ceiling and will tell you when you've hit it rather than quietly delivering lukewarm water.

Flaws but not dealbreakers

The 300-amp service requirement disqualifies most homes without a major, expensive upgrade. This is the single biggest reason to buy something smaller.

Owners report the flow rate feels restricted compared with a tank heater, which is how flow control maintains temperature. You get consistent hot water, not a firehose.

A few owners report never reaching the high temperatures they expected, especially with cold incoming water and multiple fixtures open. That's the physics of a 36 kW ceiling, but it's a disappointment if you sized by hope rather than by chart.