The Best Tankless Electric Water Heater for 2021

Choosing the best water heater for you home may seem confusing at first, you’re wondering whether to go for a tankless electric water heater or a tankless gas water heater or maybe you need a tankless propane water heater.

You’ll want to get the best water heater that’s right for your needs and of course ideally you’ll want a water heater that is going to save you money in the long term.

In this review you’ll see for yourself the best electric tankless water heater options available for whole house needs, if you require just a single point of use tankless water heater for a shower or faucet for example, then check out our review of the best tankless point of use water heaters.

Best Tankless Electric Water HeaterBrand
Best for Large Size HouseholdsRheem 240V 4 Heating Chambers RTEX-36
Best for Medium – Large Size HouseholdsEemax EEM24036
Best for Medium Size HouseholdsStiebel Eltron Tempra 29 Trend
Best for Small – Medium Size HouseholdsEcoSmart ECO 27
Best for Small Size Householdsecosmart ECO 18

The Best Tankless Electric Water Heaters Reviewed

We’ll guide you through all the relevant information and help to answer the most important questions such as, what size electric tankless water heater do I need? and how much hot water in gallons per minute (GPM) will I get from each of the recommended tankless water heaters reviewed here. Hopefully then you’ll know what to expect performance wise from an electric tankless water heater, helping you to decide which one best suits your own needs and requirements.

Best for Large Size Households: Rheem 240V 4 Heating Chambers RTEX-36

The Rheem RTEX-36 tankless electric water heater is a compact unit so it’s not going to take up valuable space in your home and has to be said that it looks pretty stylish too. Most importantly though is that it’s 99.8% energy efficient and will supply you with continuous hot water whenever you want it, and for however long you want it.

With a self modulating power control (basically, this adjusts the power according to the demand) and a maximum flow rate of 8.8 gallons per minute (GPM) this on demand electric tankless water heater is a great choice for your whole house hot water requirements.

Just how hot you want the water is all down to personal preference. The easy to read and adjust external digital thermostatic control clearly displays the chosen hot water heating temperature which can be adjusted in increments of 1°F from 80°F right up to 140°F ensuring that you always get the hot water temperature set to just how you want it.

Installing the Rheem RTEX-36 is made a whole lot easier thanks to the bottom 3/4″NPT water connections making this tankless electric water heater easy to work on, and service too.

With scheduled maintenance this tankless water heater should last many years, far longer than a standard tank water heater.

As for element part replacement, the Rheem RTEX-36 uses threaded brass topped copper immersion heating elements for durability and are easy to replace if you need to replace them in the future.

Product Information

RTEX-36 DimensionsSized In Inches
Depth3.5″
Height18.25″
Width21.63″

This is a powerful water heater and it’s important that you check with an electrician to ensure that your electric panel has room to accommodate the power requirements of this tankless water heater.

Further InformationRheem RTEX-36
Voltage 240
Kilowatts36
Amps150A
Breakers 4 X 40A
Wire Size8 AWG
Weight22.7 lbs
Install Location Indoor only
Warranty 5 Years
GPM 8.8 Maximum

What We Like:

  • Impressive GPM – With up to an impressive 8.8 gallons per minute hot water flow rate possible, of course flow rate can vary due to outlet distance from the water heater and the incoming cold water supply temperature to the water heater.
  • Powerful And Compact – This tankless electric water heater won’t take up much space unlike a conventional tank water heater.
  • Long Warranty – An impressive 5 year warranty on the heating chamber and a 1 year parts limited warranty included with the package.

Things To Consider:

  • Electrical Requirement – Are you are sure that your electric supply can handle the requirements of this water heater? If you’re not sure then get it checked out by an electrician.
  • Instant Hot Water – Yes the heating process of the hot water is pretty instant but remember it may take some time for that hot water to travel along the pipes to the outlet, especially if the outlet is a long way from the water heater.
  • Energy Saving – This tankless water heater is very energy efficient, but you might just find yourself staying in the shower a lot longer than you used to do now, with an endless supply of hot water available.
  • Water Supply Temperature – Remember the temperature of you incoming cold water supply does play a big part in GPM flow rate, the warmer the climate where you live, does effect the incoming cold water temperature.

Best for Medium – Large Size Households: Eemax EEM24036

One of the many benefits of having a tankless water heater is the amount of space that is saved by not having the traditional tank type water heating system.

This compact tankless water heater is, as you would expect, very energy efficient too with a very impressive 99.8% energy efficiency score.

Suppling endless hot water on demand, you’ll be able to run multiple outlets at the same time without water temperature loss, thanks to the self modulating technology inbuilt into this tankless water heating system.

Controlling the hot water temperature is a breeze too, with a clearly visible digital display on the front of the water heater panel where you can make temperature adjustments in 1°F increments.

Ease of installation is a big plus here, the EEM24036 comes with 3ft of electric cable included and 1/2” CF connection with an optional 1/2” NPT adaptor included too.

Maintenance as always is highly recommended to ensure you get years and years of trouble free service from your electric tankless water heater and when parts like the copper elements eventually need replacing then this is a simple task to carry out.

The heat exchanger is made from stainless steel and the heater features thermal auto protection. All the relevant certification – ETL Listed to UL 499 and CSA along with a warranty of 1 year on parts, with 5 years warranty on leaks is included for your peace of mind.

Product Information

EEM24036 DimensionsSized In Inches
Depth3.75”
Height17”
Width21”

This is a very powerful tankless water heater and as such it is essential that you have an electrical supply that can manage the requirements of running this electric on demand tankless water heater. We always advise that you ask a qualified electrician to check out your home electrical supply to confirm that you have the spare capacity required.

Further InformationEemax EEM24036
Voltage240 Volts
Kilowatts36 kW
Amperage Draw150 Amps
Elements4 X 9 kW
Breakers4 X 40 Amp (DP)
Wire Size4 X 8 AWG
Unit Weight17.4 lbs

For an idea as to how the inlet temperature effects gallons per minute (GPM) flow rate, check out the table below to see what you can expect to get.

Inlet Temp37°F42°F47°F52°F57°F62°F67°F72°F77°F
GPM3.6 3.94.24.65.15.76.57.58.8

What We Like:

  • High GPM Flow Rate – This whole house on demand tankless water heater has high flow rate capability for running multiple outlets at the same time.
  • Compact Heating System – This tankless water heater won’t use up much room compared to a tank heating system that eats up a lot of space.
  • Good Warranty – Covering parts for 1 year as you would expect, and with a 5 year warranty against leaks.

Things To Consider:

  • Power Requirements – Make sure your electrical supply is good enough for this powerful tankless water heater.
  • Plenty of Hot Water – You’ll get a continuous supply of hot water but remember it will take time for the hot water to travel from the heater to the outlet.
  • Water Inlet Temperature – Just check to see what your water inlet temperature is and our table above will show you what to expect in GPM.

Best for Medium Size Households: Stiebel Eltron Tempra 29 Trend

Energy saving is what we like to hear about because if you are saving energy then the chances are that you’re saving your hard earned bucks too.

The Stiebel Eltron Tempra 29 Trend uses around 15-20% less energy when compared to tank water heating systems. As this is a tankless electric water heater therefor only heating the water that you use, you are not heating up water that you might not even make use of (known as standby heat loss) like you do with a conventional electric water tank storage system.

Engineered in Germany this whole house on demand electric tankless water heater gives a hot water output of 68° to 140°F and features an easy to read and adjust digital display ensuring you get the desired temperature just right.

The advanced flow control makes sure that hot water is constantly maintained meaning that you won’t run out of hot water.

Space saving is achieved with this compact electric water heater, and it runs totally silent, so you won’t be disturbed when the unit is in operation.

Product Information

Stiebel Eltron Tempra 29 DimensionsSized In Inches
Depth4.63
Height16.63
Width14.5

This on demand electric water heater obviously uses less power than our recommendations for the large household electric water heaters, but we still recommend that you get your electric panel checked out by an electrician to make sure that you have the spare capacity in your panel to hook this water heater up to.

Further InformationStiebel Eltron Tempra 29
Voltage208 Volts
Kilowatts28.8 kW
Amperage Draw120 Amp (Max)
Breakers3 x 40 A (DP)
Wire Size (Min)3 x 8/2 AWG
Unit Weight24 lbs
Water Connection3/4″ NPT

What We Like:

  • Easy To Use – Simple easy to use and understand digital display, making temperature adjustment a breeze.
  • Quality Assured – German engineering for energy efficiency and reliable performance.
  • Amazing Warranty – Being so sure of the quality and reliability of their tankless water heating systems, you get a 3 year parts warranty and a 7 year leakage warranty included.

Things To Consider:

  • Right Size Water Heater – Making sure you choose the right size tankless water heater is essential to ensure you get the desired flow of hot water.
  • Electrical Supply – If your electrical supply can’t cope with this size water heater then you still have lower powered options available, check out our next review on a 27kW electric tankless water heater.
  • Input Water Temp – Most importantly check out your incoming cold water supply temperature, this will have an effect on what you can expect in hot water gallons per minute flow output.

Best for Small – Medium Size Households: EcoSmart ECO 27

Choosing the right size tankless water heater can be a tricky process, especially if you are planning for the future where maybe your hot water needs will increase.

Aimed at the small to medium sized households the EcoSmart ECO 27 is an energy efficient electric tankless water heater that when installed as per the recommended specifications will provide you with continuous hot water on demand giving you between 2.7 and 6.5 gallons per minute flow rate depending upon your inlet water temperature.

As an example as to what you can expect from this electric tankless water heater, lets say that your inlet water temperature is a cool 37 degrees, the EcoSmart ECO 27 will give you around 3 gallons of hot water per minute at this low inlet temperature.

So if your inlet water temperature is warmer, then you’ll get more gallons of hot water per minute.

Setting the desired hot water temperature is easy, with the clear digital display panel showing the selected temperature, any adjustment from 80 -140° F can be made in 1 degree increments. The advanced flow control system makes sure you get constant hot water on demand, no more running out of hot water.

This is a compact tankless water heater so it won’t be eating in to valuable space, it’s also super silent when it is heating up the water.

Product Information

EcoSmart ECO 27 DimensionsSized In Inches
Depth3.75
Height17
Width17

The next bit is the all important information with regard to hooking this water heater up to your electrical supply, as we always say, get an electrician to confirm to you that your electric panel has the capacity to cope with the electrical demands of this 27kW unit.

Further InformationEcoSmart ECO 27
Voltage240 Volts
Kilowatts27 kW
Elements3 X 9 kW
Amp Draw113 Amps
Breakers3 X 40 A (DP)
Wire Size3 X 8 AWG
Unit Weight13.75 lbs
Water Connection3/4” NPT

What We Like:

  • Great Tankless Water Heater – This is a really capable hot water heating system, ideal for small to medium sized households that want a constant flow of hot water on demand.
  • Energy Efficient – Boasting an energy efficiency of 99.8%.
  • Easy To Use – Simple easy to use controls and digital display to make sure you get the hot water temperature you desire.

Things To Consider:

  • Inlet Water Temperature – The inlet cold water temperature does make a big difference to the output hot water flow rate, the warmer the inlet water temperature means a better GPM output flow rate.
  • Electrical Requirements – This is most important thing to get right, making sure your electric panel has the spare capacity for an additional 3 X 40 Amp breakers to supply the 27 kW of power required to keep you supplied with constant hot water on demand.

Best for small Size Households: ecosmart ECO 18

Making sure you have enough hot water for your home whether it’s a large house or a small house is an important requirement and does take a bit of planning.

What tends to happen is that most people underestimate just how mush hot water they use. It’s not the amount of hot water used throughout the day that is the concern, it’s the amount of hot water used at the most busiest times of the day that really matters.

The busiest time of the day for most households is the morning time, you wake up run the shower, run the faucet, maybe put the dishwasher on or washing machine, this is when you are using the most hot water and this busy time hot water usage is when you need to work out just how much hot water is being called for.

The EcoSmart ECO 18 tankless water heater will provide you with between 1.8 and 4.3 gallons per minute of constant hot water, the actual amount of hot water flow will depend on the temperature of the cold water supply that comes into your home.

The warmer the cold water supply to your home is, the more gallons per minute of hot water flow rate you will have.

As an example, let’s say that the temperature of the incoming cold water supply is 62° F, the EcoSmart ECO 18 electric tankless water heater will provide you with around 2.5 gallons per minute of constant hot water.

As for what that gives you in terms of water usage is one shower with a regular flow rate of 1.5 gallons per minute and a sink using 1 gallon per minute.

Controlling the hot water from between 80° F – 140° F is just a simple matter of adjusting the digital setting which is clearly displayed on the front of the unit. Adjustments to the hot water temperature can be made in increments of 1° F.

Product Information

EcoSmart ECO 18 DimensionsSized In Inches
Depth3.75
Height17
Width14

Getting the electrical part of the job right is really important, we recommend that you get a qualified electrician to check your electric panel to make sure that you have spare capacity in the panel to accommodate the power requirements of this tankless water heater.

Further InformationEcoSmart ECO 18
Voltage240 Volts
Kilowatts18 kW
Elements2 X 9 kW
Amp Draw75 Amps
Breakers2 X 40 Amp (DP)
Wire Size2 X 8 AWG
Unit Weight11.25 lbs
Water Connection3/4″ NPT

What We Like:

  • Ideal For Small Home Usage – Compact and efficient tankless water heater.
  • Excellent Value For Money – Getting enough constant hot water for your home usage doesn’t have to be expensive, this tankless water heater offers great bang for your buck.
  • Lower Power Requirements – Compared to the bigger sized tankless hot water heaters, this unit shouldn’t be a problem when it comes to connecting the power to your electric panel. We always recommend that you get any electrical work carried out by a fully qualified electrician.

Things To Consider:

  • Enough Flow Rate – This is what most people underestimate which results in them being disappointed with the amount of hot water that is produced.
  • Instant Hot Water – That is what we want, instant hot water but remember that the water has to travel along the pipe from the tankless water heater to the outlet point. You won’t get hot water the instance you turn the faucet or shower on, you may have to wait quite some time for that hot water to finally show up especially if the outlet is some distance from the tankless water heater.


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