Best Electric Tankless Water Heaters (2026)

WINTEMP's 18kW unit is ETL certified, self-modulating and WiFi enabled, with a listed 4.3 GPM maximum and a plain note that you need 150 amp household service. Self-modulating means it adjusts element power to the incoming water temperature and flow, so you are not paying for full power when only a trickle is running.

Its value is in the honesty of its requirements. At 18 kW it draws about 75 amps, so you need a double-pole breaker near 100 amps and 4 AWG or heavier copper. Against the NOVIEEX 18kW it lists less flow, and against the 27kW unit it uses a much smaller breaker.

Ownership is simple: no vent, no combustion check. Descale the heater yearly in hard water, keep the inlet screen clean and have the lugs checked, since high-amp connections run warm if they loosen. Before ordering, photograph the inside of your panel and send it to an electrician, because the number of open slots and the size of the main breaker settle the question faster than any listing.

The NOVIEEX 18kW lists up to 4.9 GPM, which is higher than the WINTEMP 18kW at 4.3 GPM despite identical electrical power. Since power determines how much water you can heat by a given rise, the extra flow is a best-case figure at a small temperature rise, not a different physics.

That makes it the unit to compare carefully. It is aimed at two to three fixtures in a small or medium home, and at the same 75 amp load. The gap between 4.3 and 4.9 GPM tells you to read the test rise in the manual, since the same elements cannot make an extra 0.6 GPM at the same rise.

Ownership is the usual descale, screen and connection checks. Because the brand is newer, keep the receipt and confirm warranty terms. If you do buy it, ask the seller for the test conditions behind the 4.9 GPM figure, since a reputable maker can state the temperature rise it used.

The 27kW WINTEMP is the high-capacity unit here, listed up to 6.5 GPM and requiring 200 amp household service. At 240V it draws about 112 amps, which means multiple double-pole breakers or a single large one and very heavy wire.

It is the only electric in this lineup that can handle three bathrooms in a mild climate, and it still falls short in a cold one. At a 70F rise, 27 kW gives only about 2.6 GPM by the standard formula, which is why the stated 6.5 is a best case that needs a small rise. Compared with the Rheem RTEX-24 it has a bit more capacity and a stated panel requirement.

Ownership requires an electrician for the wiring, a descaling routine and a check of the connections. If the panel is marginal, the upgrade can cost more than the heater itself. Add a dedicated shutoff and a pressure relief valve if local code requires them, and plan the wall space so the cover can come off for service.

The ORBEK 14kW lists 3.38 GPM, a note that the household panel must have at least 150 amps total capacity, a three-second heat-up and a 98 percent efficiency figure. Electric resistance heating is close to 100 percent efficient at the heater, so that number is believable, but it says nothing about the cost of electricity.

It sits between the Rheem 8kW and the 18 kW units, drawing about 58 amps. That is enough for one shower plus a tap in a mild climate, and it suits a condo or an addition. Against the WINTEMP 18kW it has about three-quarters of the flow and a lower breaker size.

Ownership is routine. Descale yearly, keep the inlet screen clean and check connections. The panel note is the real practical hurdle. A heater this small is also easy to carry upstairs and mount, which makes it practical for a retrofit where the old tank location is cramped.

Rheem's RTEX-13 has an external adjustable digital thermostat accurate to one degree, two copper immersion elements that can be replaced in the field, self-modulating power control and half-inch NPT adapters in the box. At 13 kW it draws about 54 amps.

Field-serviceable elements are the ownership story. A burned-out element on a sealed unit often means replacing the whole heater, but on this model you can swap one. The data does not list a GPM, so check the sizing chart in the manual, and expect a rating near 2.5 to 3 GPM in warm climates.

It is an established brand with wide parts availability. Descale yearly, keep the screen clean and check the connections.

The 8kW Rheem is the smallest whole-house-style heater in the group, rated up to 1.95 GPM at about 33 amps. That is enough for one low-flow shower or a couple of sinks, and it fits a panel that would not tolerate the larger units.

Its limit is flow. Two simultaneous taps will leave the water lukewarm, and in a cold climate even one shower may be marginal. Against the Rheem RTEX-13 it has a bit over half the power and a lower breaker size.

Ownership is routine: a yearly descale, a clean screen and secure connections. It suits a small apartment, a cabin or a bathroom addition. Because the unit is the smallest here, treat it as a point-of-use or single-bath solution and avoid sharing it between a shower and a kitchen.