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Best Electric Tankless Water Heaters of 2021

Looking for an energy-efficient alternative to a traditional water heater? In this review, you’ll find the best electric tankless water heaters on the market.

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Best Electric Tankless Water Heater Reviews of 2021

Stiebel Tempra 36 Trend

Stiebel Eltron Tempra 36 Trend Tankless Water Heater

Best for heavy-duty demands

Its continuous flow technology makes it easy to take long showers or use hot water for chores without any worries at all.

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1 Stiebel Tempra 36 Trend Review

Whether you love taking long, soothing showers or need an endless supply of hot water for your business, the Stiebel Tempra 36 Trend could be the best electric tankless water heater you can get.

Its greatest highlight is the self-modulating technology developed to save energy. Three water temperature levels – with temps varying from 68°F to 140°F – also make it easy to save energy even more by preventing overheating based on your purpose.

We also like its silent operation and that it’s easy to install. The heater needs no venting, so you can place it in a windowless kitchen or bathroom. Moreover, an intuitive control panel and memory functions bring further value.

Performing, eco-friendly, and easy to use, this is the best electric tankless water heater for small apartments and big houses alike.

Best value
EcoSmart ECO 27

EcoSmart ECO 27 Electric Tankless Water Heater

Best for most people

The digital temperature control ensures easy programming of the desired settings.

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2 EcoSmart ECO 27 Review

Almost as energy efficient as our best-in-class pick, the EcoSmart ECO 27 is perfect for both residential and commercial use in the northern areas where incoming water temperatures can be as low as 37°F.

Equipped with a self-modulating technology, the system helps reduce your hot water bills with up to 50% and is capable of heating as much as three gallons per minute in low temperatures.

This electric tankless water heater is also perfect for high-demand applications, and at warmer temperatures, it is suitable to run multiple sinks and showers simultaneously.

Easy to control from the digital control panel, the water heater allows for 1° increment from 80°F to 140°F.

Great energy efficiency, suitability for high-demand applications and fairly easy to install, the EcoSmart ECO 27 is the best electric tankless water heater for the money.

Also great
Rheem RTEX-18

Rheem RTEX-18 18kW 240V Electric Tankless Water Heater

Easy temperature control

The simple, one-knob control panel with temperature display makes it a cinch to operate.

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3 Rheem RTEX-18 Review

If you’re looking for a digital electric tankless water heater for a smaller home, the Rheem RTEX-18 is a great alternative. Designed with lower-volume demands in mind, it can supply sufficient hot water for a 3-4 people household.

Like our best in class and best value, it provides hot water on demand, providing around 1.5 gallons of hot water per minute at 82°F rise. While this rate could be insufficient if you plan to run multiple faucets simultaneously – or for a high-volume bathtub – it is more than enough for most domestic needs.

Operation-wise, the unit has only one knob that makes it a cinch to control, and we like its slimline design that fits well in small spaces. No doubt, a great choice for a smaller household.

Best budget
Bosch ES4 Tronic 3000 T

Bosch ES4 Tronic 3000 T Electric Mini-Tank Water Heater

Small and inexpensive

Wall, floor, or shelf installation options make this tankless water heater perfect for dorms and studio apartments.

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4 Bosch ES4 Tronic 3000 T Review

Whether you’re on a budget or need a versatile solution for a really small apartment, the Bosch 3000 T fits the bill. It isn’t as technological or good looking as the digital electric water heaters, but it does what it’s supposed to do and comes at a fraction of the price.

Despite its compact size – it is small enough to fit under the sink – it provides sufficient hot water for two points of use at a time.
It is also very easy to install without the help of a plumber and is energy efficient. The analog control isn’t fancy but is intuitive and functional. Overall, an excellent choice for small budgets and small homes.

1. Gas vs. electric tankless water heaters

Tankless water heaters offer an energy-efficient alternative to the conventional tank water heaters and can be either gas-powered or electric.

  • Gas tankless water heaters: Run on either propane or natural gas and typically heat water at a faster rate than their electric counterpart. A gas tankless water heater can output around 11 gallons per minute (GPM) of hot water, but they require proper environmental ventilation for safe
  • Electric tankless water heaters: Typically connect to the 240V circuit and have a lower performance than the gas units. However, they don’t emit any noxious fumes, which means you can install them anywhere without worrying about ventilation.

Why invest in an electric tankless water heater?

Besides installation versatility, there are a few other reasons you should choose an electric tankless water heater.

  • Electric units have more competitive prices than the gas heaters.
  • Can be used with alternative power sources including solar energy and power generators.
  • They need lower maintenance.

2. Electric tankless water heater power

Electric tankless water heaters, also called on-demand water heaters, are designed to heat water instantly and require a high surge load to do so. Most units require either a 208V or 240V single phase circuit and sufficient amperage to support the operation.

The exact power requirements of a system depend on the flow rate and heating capacity of the unit. Small, medium and large heaters running on 240V typically require:


Flow rate in gallons per minute

50 amps

2.5 GPM

100 amps


150 amps

7.5 GPM

3. Flow rate

The flow rate determines the efficiency of an electric tankless water system and is measured in gallons per minute (GPM). This number helps you determine whether or not a specific unit is suitable for your home.

The GPM flow rate represents the gallons of water the system can heat in a minute, and most electric tankless water heaters have a GPM rating between 1.5 and 9 gallons.

4. Sizing your electric tankless water heater

Knowing the GPM rate of your water heater is insufficient. To determine the right size, you must consider the climate you live in and the hot water demands of your home.

How many GPM do you need?

The easiest way to determine how many GPM you need is by calculating your household’s peak water demands. Peak water demands refer to the hot water consumption (calculated in gallons per minute) when hot water is used by multiple fixtures and appliances at a time.

Modern fixture and appliances have this information disclosed in their manuals, but in case you don’t know them, it’s safe to assume the following GPM demands:

Fixture / Appliance

Hot water demands

Kitchen or bathroom sink

0.75-2.5 GPM


1.2-3.5 GPM


1-2 GPM

Washing machine




Because old fixture and appliances use more water than the new ones, you can get a more accurate idea of the real GPM demands by timing how long it takes a fixture to fill a one-gallon bucket.

To determine your needs, sum up the water demands of the fixtures and appliances which are likely to run at the same time and add at least one more gallon to ensure your system can supply a steady flow of hot water.

Temperature rise requirements

Besides GMP demands you must also determine the rise in temperature you require by subtracting the temperature of the incoming water from the desired temperature of the output water.

How hot must the water be?

Most residential applications require water heated to around 105-120°F. Commercial applications may require hotter water, typically between 120 and 140°F.

By knowing how hot you want the water to be and the incoming temperature of the water, you can assess the desired heating capacity of the water heater.

Some systems allow you to measure the incoming water temperature accurately via a thermostat, but if you don’t have one, it is recommended to assume the incoming water has a temperature of around 50°F. 

How to assess the size?

With the numbers above you can determine the right size of the electric tankless water heater. For instance, if you need to heat water from 50°F to 105°F for running a low-flow shower, you will need a heater capable of producing a 55°F temperature rise at a flow rate of at least 2.2 gallons per minute.

Most electric tankless water heaters come with clear size specifications, and the best electric tankless water heaters can provide over 80°F temperature increments depending on the incoming temperature and flow rate.

5. Energy efficiency

Electric tankless water heaters provide a greater energy efficiency than the conventional systems through self-modulating technologies that use the least possible energy to heat the water.

What is self-modulating technology?

The self-modulating technology allows the tankless water systems to activate at low flow rates of around 0.25 GPM and modulate the energy consumption based on the temperature of the incoming water for maximum efficiency.

These systems typically cut off the alimentation with energy as soon as the water ceases to flow.

An energy-efficient system with self-modulating technology can typically reduce your hot water bills with up to 60%, which usually lowers the overall electricity costs with up to 20%.

6. Other important features

Besides all the above, there is a series of other important features you must check before buying.

  • Design: The main advantage of the electric tankless water heaters is their slim and compact design which allows for a versatile However, if you want to install the unit in a restricted space, it is a great idea to check the overall size of the system you like to make sure it fits.
  • Temperature controls: Electric water heaters can have analog or digital temperature controls. Analog units are typically cheaper but setting an exact temperature is near impossible. Digital units allow for a better temperature control.
  • Fahrenheit/Celsius scales: The best electric tankless water heaters show the temperature in both Fahrenheit and Celsius degrees for a better understanding of the temperature by all users.
  • Display: A nice feature to have if you want to keep an accurate track of the set water temperature. LCDs typically equip the digital units, but some water heaters with analog controls may also use an LCD screen to display the temperature.

7. The Best Electric Tankless Water Heater for the Money

Best value
EcoSmart ECO 27

EcoSmart ECO 27 Electric Tankless Water Heater

Best for most people

The digital temperature control ensures easy programming of the desired settings.

Check price on Amazon

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