Best Electric Tankless Hot Water Heater

A storage water heater can leave the last person in the house standing under a stream that turns cold without warning. An electric tankless heater takes a different route. It heats water as it passes through the cabinet, so long showers are not limited by the amount stored inside a tank.

The Stiebel Eltron Tempra 36 Plus is the best electric tankless hot water heater for most homes that have enough electrical capacity. Its 36-kilowatt output, automatic flow control, quiet operation, and steady outlet temperature make it a strong whole-house pick. The Rheem RTEX-36 offers high rated flow at a lower purchase price, while the EcoSmart ECO 36 suits warm regions and new homes built around its heavy electrical demand.

Best Electric Tankless Water Heaters at a Glance

Best Overall: Stiebel Eltron Tempra 36 Plus

The Stiebel Eltron Tempra 36 Plus earns the top spot because it handles overloaded demand better than many competing electric units. When too many faucets open, its automatic flow control can reduce the stream rather than allowing the outlet temperature to fall.

That response matters during a shower. A normal electric tankless heater may begin sending cooler water when a second fixture opens. The Tempra 36 Plus attempts to protect the selected temperature. The shower stream may become softer, but it should remain warm.

The unit has a 36-kilowatt rating and can draw up to 150 amps at 240 volts. It normally needs three 50-amp double-pole breakers and three heavy copper wire runs. Those numbers place a large burden on the home’s electrical service.

A modern 200-amp panel may still lack room once the range, dryer, air conditioner, oven, vehicle charger, and other large loads are counted. Some homes may need a service upgrade. That work can cost more than the heater itself.

The Tempra 36 Plus has no burner, exhaust pipe, pilot flame, or fuel line. It mounts on a wall and remains silent while running. The front dial allows outlet settings between 86°F and 140°F.

Its 3/4-inch water connections suit whole-house plumbing. The cabinet is much smaller than a storage tank, which can free a closet or utility-room corner for other use.

Cold groundwater remains the main limit. In a warm region, the Tempra 36 Plus may feed two showers and a sink under moderate conditions. In a northern winter, the same heater may be comfortable with one strong shower and one light faucet.

Best match: A smaller or medium home with a large electrical service, moderate simultaneous demand, and no natural-gas connection.

Best High-Flow Pick: Rheem RTEX-36

The Rheem RTEX-36 is another 36-kilowatt whole-house heater. Rheem lists a rated flow of up to 8.8 gallons per minute, though that top figure depends on warm inlet water and a modest temperature increase.

The heater uses self-modulating power. It turns on only the heating capacity needed for the water passing through it. A bathroom faucet calls for less power than two showers, so the unit adjusts its electrical draw to match the load.

The digital display and front dial make temperature changes easy. Bottom-mounted 3/4-inch water connections can help with a wall installation near the old tank pipes.

The RTEX-36 can work well in southern states where groundwater arrives warm for much of the year. A home in Florida, Texas, or Arizona asks the heater to add fewer degrees than a home in Maine or Minnesota.

Its headline flow number should not be treated as a promise for every home. A heater that produces close to 8.8 GPM with warm inlet water may provide far less when incoming water sits near 40°F.

Check the main service before purchase. A large electric tankless model may need several open breaker positions, thick copper wire, and a service upgrade. The small wall cabinet can hide a very large electrical appetite.

Best match: A warm-region household that wants high rated flow and familiar Rheem controls.

Best for Warm Climates: EcoSmart ECO 36

The EcoSmart ECO 36 has a 36-kilowatt heating rating and a compact metal cabinet. It draws up to 150 amps at 240 volts and calls for four 40-amp double-pole breakers.

EcoSmart advises a 300-amp household service for this model. That recommendation alone should stop buyers from ordering before an electrician sees the panel. Many homes have 100- or 200-amp service and cannot carry this heater without costly changes.

The ECO 36 uses four heating chambers and copper heating parts. Its 0.3-GPM activation rate is lower than that of many whole-house units. This can help the heater turn on during a light faucet draw.

The front control allows one-degree temperature changes from 80°F to 140°F. The unit also carries a limited lifetime warranty when registration and written terms are met.

EcoSmart’s own flow chart shows why climate matters. With 40°F inlet water, the ECO 36 is rated near 3.8 GPM at a 105°F outlet. With 70°F inlet water, the rating rises to about 7.0 GPM.

That difference can mean one shower in a cold region or two showers plus a faucet in a warm region. The heater has not changed. The amount of heat needed for each gallon has changed.

Best match: A new home in a warm climate with a 300-amp service or an electrical design built around the heater.

Best Bosch Model: Tronic 6100 C

The Bosch Tronic 6100 C is a whole-house electric tankless line with thermostatic modulation. Its heating elements adjust output as water flow and inlet temperature change.

Bosch lists 95% thermal efficiency, 3/4-inch water fittings, a built-in inlet filter, and a five-year limited warranty. The inlet filter can catch debris before it reaches the heating chamber.

The simple front temperature control suits buyers who do not want app pairing or a long menu. The heater has no fuel pipe and needs no exhaust vent.

Model size still matters. Bosch sells more than one output level within the Tronic 6100 C line. The smaller version suits lighter household demand, while the larger version can serve more fixtures in a warm region.

A Bosch dealer or electrician should compare the selected model with the home’s winter inlet temperature and available service capacity. Buying the largest model without checking the panel can turn a compact heater into a costly electrical project.

Best match: A buyer who wants a whole-house Bosch unit with simple controls and a built-in water filter.

Best 27-kW Pick: Rheem RTEX-27

The Rheem RTEX-27 lowers the heating output from 36 kilowatts to 27 kilowatts. That reduces the electrical load, though it also reduces the amount of water the heater can warm each minute.

A 27-kilowatt model can suit a small home, apartment, cabin, or warm-region property where two heavy fixtures rarely run together. It may also fit a household with low-flow shower heads and careful water use.

The smaller electrical load does not make installation minor. A unit in this class still needs several large double-pole circuits and thick copper wire. An electrician must check available panel capacity.

Cold-region buyers should be cautious. A 27-kilowatt heater may serve one shower well during winter but struggle when a kitchen faucet opens at the same time.

Check the Rheem RTEX-27 on Amazon.

Best match: A one-bathroom home in a mild climate or a household with light peak demand.

Best Point-of-Use Pick: Stiebel Eltron DHX 15-2 Plus

Not every buyer needs one heater for the whole house. A point-of-use model can sit near a remote bathroom, workshop sink, garage faucet, cabin, or guest suite.

The Stiebel Eltron DHX 15-2 Plus is made for this job. It can feed more than one sink, and it may support a low-flow shower where incoming water is warm.

Its automatic flow control can reduce water flow when demand rises beyond the unit’s heating capacity. The activation rate is only 0.264 GPM, which helps with low-flow faucets.

The front display shows temperature and flow information. Two memory buttons allow quick changes between preferred settings. A control lock and scald guard can limit unwanted temperature changes.

This model is not a normal whole-house choice. It works better close to the fixtures it serves. Short pipe runs also reduce the wait for warm water at a distant sink.

Check the Stiebel Eltron DHX 15-2 Plus on Amazon.

Best match: A remote bathroom, cabin, guest area, workshop, or group of nearby sinks.

How an Electric Tankless Water Heater Works

Cold water enters the heater after a faucet opens. A flow sensor detects movement and switches on the heating elements. Water passes through heated chambers and leaves at the selected outlet temperature.

The unit stores little or no hot water. Close the faucet and the elements switch off. Open it again and heating begins.

This design removes standby heat loss from a large tank. It also removes the waiting period tied to tank recovery. The limit is heating power per minute rather than stored gallons.

Why Incoming Water Temperature Matters

Electric tankless sizing begins with temperature rise. Subtract the inlet-water temperature from the desired outlet temperature.

Water entering at 70°F and leaving at 105°F needs a 35°F rise. Water entering at 40°F and leaving at 105°F needs a 65°F rise.

The second home asks the heater to add almost twice as much heat to every gallon. Flow must fall when the heater reaches its maximum electrical output.

This is why one model can serve several fixtures in a warm state but only one shower during a northern winter.

How Many GPM Does Your Home Need?

A standard shower head may use about 2.5 GPM. A low-flow shower may use 1.5 to 2.0 GPM. Bathroom faucets often draw less, while kitchen faucets can use close to 2.0 GPM.

Add the fixtures that may run together. Two 2.0-GPM showers create 4.0 GPM of demand. Add a 1.5-GPM faucet and the total reaches 5.5 GPM.

The heater must produce that flow at the home’s winter temperature rise. A box that says “8.8 GPM” may not provide 5.5 GPM when inlet water is close to freezing.

Check the Electrical Panel Before Buying

Electrical capacity is the biggest obstacle for a whole-house electric tankless heater. A 36-kilowatt model can draw 150 amps while running at full output.

Many homes have 100- or 200-amp service. The heater must share that service with cooling, cooking, laundry, lighting, vehicle charging, and every other electrical load.

The panel also needs enough open spaces for several double-pole breakers. Each circuit needs heavy copper wire between the panel and heater.

A service upgrade, larger panel, meter work, and new feeder cable can push the job well past $2,000. Get an electrician’s written price before ordering the unit.

Electric Tankless or Heat Pump Water Heater?

An electric tankless heater saves wall and floor space. It also avoids stored-water limits and needs no room air or condensate drain.

A heat pump water heater uses far less electrical power at one moment. It stores water in a tank and warms it slowly by drawing heat from nearby air.

Homes with a 200-amp panel may accept a heat pump tank more easily than a 150-amp tankless unit. The heat pump needs floor space, room air, and a drain for condensation.

Electric tankless works best where space is tight, demand is modest, and electrical capacity is generous. A heat pump tank often makes more sense for a larger family that wants lower yearly electricity use.

Installation Costs People Miss

The heater price may be the smallest part of the job. Added costs can include breakers, copper wire, conduit, panel work, service upgrades, shutoff valves, plumbing changes, permits, wall repair, and labor.

Long wire runs cost more because large copper cable is expensive. A heater mounted far from the main panel may erase much of the price advantage of a compact unit.

Ask the electrician and plumber for one complete installed price. Buying the unit before those visits can leave an expensive box that the home cannot power.

Care and Hard Water

Minerals can collect inside the heating chambers. Hard water may leave a chalky coating that slows heat transfer and narrows water passages.

Periodic flushing may be needed, based on water hardness and the maker’s directions. Inlet screens should also be checked for sand, rust, and pipe debris.

A scale-control cartridge or water softener may help in severe hard-water areas. Ask a local water-treatment company or plumber which option fits the water supply.

Common Buying Mistakes

The first mistake is buying by maximum GPM alone. Flow at the needed temperature rise gives a better picture.

The second mistake is ignoring the electrical panel. A large heater can require most of a 200-amp service by itself.

Another mistake is choosing a model that is too small for winter demand. Long showers may remain warm, but opening a second fixture can weaken the stream or lower the outlet temperature.

Some buyers also expect a tankless unit to deliver instant warm water at every faucet. Water still has to travel through the pipes. A distant bathroom may wait just as long unless the heater sits nearby.

Which Electric Tankless Hot Water Heater Should You Buy?

Choose the Stiebel Eltron Tempra 36 Plus for the best whole-house package. Its automatic flow control gives it an edge when household demand rises beyond the heater’s limit.

Choose the Rheem RTEX-36 when high rated flow and simple digital controls matter most.

Choose the EcoSmart ECO 36 for a warm-region home with a 300-amp electrical service or new construction designed around its 150-amp draw.

Choose the Bosch Tronic 6100 C when you want simple operation, a built-in inlet filter, and a five-year limited warranty.

Choose the Rheem RTEX-27 for a smaller home with modest peak demand. Choose the Stiebel Eltron DHX 15-2 Plus for a remote bathroom, cabin, workshop, or group of nearby sinks.

The best electric tankless water heater should match the home’s winter inlet temperature, simultaneous water demand, main service size, panel space, and installation budget. When those pieces line up, a small wall-mounted cabinet can provide long-lasting hot water without a bulky storage tank taking up the room.