How to Install an Electric Tankless Water Heater + Installation Requirements

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Buying an electric tankless water heater is only the first step. The unit must also be properly installed in your home.

This job calls for good plumbing and electrical skills, and might better be done by a licensed professional (even required in some areas).

However, if you prefer to install your new water heater DIY-style, be prepared to spend a couple of hours in order to finish the whole setup.

Want to learn all the details? The following guide explains how to install an electric tankless water heater step by step.

Key Takeaways

Before getting started, check if your home can handle the amp draw of an electric tankless water heater. Ask your electrician or check your electrical breaker box

How to Install:

  1. Turn off all involved circuit breakers and close the main water supply (drain and disconnect the old water heater if necessary)
  2. Take off the front cover of the unit and mount the electric tankless water heater to a wall
  3. Establish the cold (usually right side) and hot (usually left) water connections. (Tip: Install a shut-off valve before and after the heater for easier maintenance)
  4. Open several hot water outlets for a couple of minutes to purge any air from the pipes and water heater and check all connections for leaks
  5. Refer to the manual for the wiring of the electrical connections
  6. Reattach the front cover and turn on the circuit breakers.
  7. Turn on the electric tankless water heater and configure it according to your preferences.
  8. Open a hot water outlet, wait until the temperature has stabilized, and make adjustments if necessary.

Electric Tankless Water Heater Installation Requirements

What are the requirements to install an electric tankless water heater?

Electrical Service Requirements

Not every home is suited for a whole house electric tankless water heater. This is because the amp draw of such a system is simply too high. For example:

The Stiebel Eltron Tempra 36 Plus requires 3 separate dedicated 50A double pole breakers and a recommended main service of at least 300A. To put this into perspective, the average home has a total capacity of 200A.

This could mean that you have to upgrade your old electrical service panel with bigger wires and bigger breakers, or you have to run a completely new one entailing a couple of thousand dollars worth of electrical work.

FYI: The Stiebel Eltron Tempra 36 Plus can provide 5.45 gallons per minute at 59 °F feed water and 105 °F output water temperature.

Stiebel Eltron Tempra 36 Plus

Stiebel Eltron Tempra 36 Plus – Available on

The Tempra 24 Plus which is somewhat smaller still requires 2x 50A double pole breakers and 150A main service.

A point-of-use (POU) electric tankless water heater should not be a problem in terms of amperage requirements. Also, while most require 240V power, some very small POU units can run on 120V.

How to determine the current size of your home’s electrical service? Check the electrical breaker box that can usually be found outside the house. You could also look for a label in your electrical panel. Another option would be to ask your electrician.

Water Pressure Requirements

Most electric tankless water heaters can work at a pressure range between 30 and 150 psi. If the incoming water pressure is above 150 psi a pressure reducing valve must be installed upstream of the heater.


As a homeowner you are usually allowed to install a water heater yourself. However, in most states you must still pull a permit to have it inspected for safety. This also goes for replacing an old water heater.

A plumbing inspector will come to your place and look at the installation to make sure that the work was done properly.

Where to Install

The first step is to find an appropriate wall to mount the water heater to. For a whole house water heater, it makes sense to place it close to where most hot water is being used. This will allow you to get warm or hot water faster when you open an outlet (doesn’t matter if you use a recirculation pump; more info below). At the same time, you have to have access to the main cold water line.

For point of use systems, you want to place them as close to the point of usage as possible so the water reaches the outlet in a timely manner.

The good news is that electric water heaters don’t need venting. And because we don’t have a storage tank we can choose a location where a tank-based unit may not fit – think small bathroom or even under sinks.

Just keep in mind that most electric tankless water heaters must be installed vertically with the power and water supply connections pointing downward. Also, there must be minimum clearance for servicing.

Generally speaking, you should avoid locations where

  • Your water heater would routinely be splashed with water or other liquids.
  • Freezing temperatures can occur.

Equally problematic are excessive moisture and humidity.

Failure to comply with this will likely void your product warranty.

Tools & Supplies

Tools and supplies you need to successfully install your new electric tankless water heater may include the following:

You haven’t purchased a system yet? Definitely check out our electric tankless water heaters reviews to find the best one! You can learn how to properly size an electric tankless water heater here.


  • Drill + drill bits
  • Flat head screwdriver
  • Phillips head screwdriver
  • Needle nose pliers
  • Adjustable wrench
  • Pipe cutter
  • Pencil
  • Tape measure


  • Mounting screws and anchors (should be provided with system)
  • Piping, ¾” or ½” (e.g. copper pipe or stainless steel flex pipe)
  • Shut-off valves
  • Pressure reducing valve
  • Temperature and pressure relief valve (T&P)
  • Teflon tape
  • Sand paper
  • Pipe insulation
  • Double pole circuit breakers
  • Wire + ground
  • Recirculation pump + cross-over valve

In addition you might need tools and supplies for soldering.

plumbing wrenches

How to Install an Electric Tankless Water Heater Yourself Step by Step

Before you get started, please note that this step-by-step installation guide is only meant as an example. The required steps to set up your specific water heater may vary. Thus, make sure that you read the entire product manual.

What’s more, improper installation will likely void the warranty, may decrease system lifespan, and could result in serious personal injury or death. So if you don’t know what you are doing, do yourself a favor and hire a licensed electrician and plumber to do the install for you. The job is too dangerous and not worth the risk just to save a few hundred bucks.

On a side note, with some manufacturers their systems must be installed by a licensed contractor or else the warranty will void automatically.

And lastly, if you have any questions regarding the installation call tech support.

Disclaimer: It is recommended that this job is done by a licensed professional. Furthermore, the installation must comply with all national, state and local electrical and plumbing codes.

  1. First of all, turn off all involved circuit breakers.
  2. Close the main water supply.
  3. Drain and disconnect your old water heater if necessary.
  4. Remove any screws that secure the front cover of the unit that you want to install. Take off the front cover, but be careful: You might have to remove one or more plugs before you can set it aside.
  5. Mount the electric tankless water heater to the wall. Screws and anchors should be included in the package
  6. Now it’s time to establish the cold (usually right side) and hot (usually left side) water connections. It’s probably easiest if you use stainless steel flex pipe (¾”) in combination with Teflon tape for this. Alternatively, you could use copper or PEX tubing (should be rated for high temperature applications). It’s just that some water heaters come with a filter screen at the cold water inlet that requires cleaning every once in a while. This is why it’s important that the cold water connections can be easily removed. If you have to cut into a pipe, clean the edges. And when soldering, remember to flush the pipes before connecting them to the water heater and that excess heat can cause damage to the unit.
    • It is recommended to install a shut-off valve before and after the heater so that you can turn off the water supply to the unit for maintenance works etc. without shutting off the supply to the rest of your home.
    • By the way, this is also the right time to install a pressure reduction valve on the cold water side in case the incoming water pressure exceeds a certain threshold (read more). A temperature and pressure relief valve (T&P) – to be installed on hot water side – should not be required, unless prescribed by local or state installation codes.
  7. Open several hot water outlets for a couple of minutes to purge any air from the pipes and water heater. Meanwhile, you can check all connections for leaks. Close all outlets.
  8. Attention: Refer to wiring diagram in manual! The next step is to make the electrical connections with the water heater on one side and the electric panel on the other. For the correct wire and circuit breaker number & size, refer to the manufacturer instructions. Small units can be connected to a single circuit using one set of 6/2 AWG wire and ground protected by a 50A double pole breaker, for example. Larger units require two or even three separate circuits and possibly thicker wire. Cut each wire set to length and strip, feed it through the bottom holes of the water heater housing, and firmly attach it to the appropriate slots on the terminal block (check manufacturer instructions for optimal torque). For each circuit, a ground conductor must be connected to the unit’s grounding busbar and the circuit breaker panel.
  9. Double check all electrical connections. Make sure that you did not mix up the different wire sets.
  10. Reattach the system’s front cover.
  11. Turn on the circuit breakers.
  12. Your electric tankless water heater should now be turned on. Configure it according to your preferences, e.g. adjusting the water temperature to the desired level.
  13. Open a hot water outlet. Wait until the temperature has stabilized. Check the temperature and adjust if need be.
  14. Done!

Installation Video

Prefer video? You might find this helpful:

Additional Comments

Lastly, some additional comments:


You can learn more about how much electric tankless water heaters cost here.

Insulation on Hot Water Pipes

Low-hanging hot water pipes coming from the water heater should be insulated to protect children from burns.

Installing Water Recirculation

Even with a tankless a.k.a. instantaneous water heater, you won’t have instant hot water whenever you open the kitchen faucet or another outlet. This is because the hot water sitting in the pipes will eventually cool down if you don’t use it.

Fortunately, there is a solution to this: A recirculation pump. A recirculation pump circulates the cooled-off water back to the heater to heat it once more. This has a couple of advantages:

  • You only have to wait a few seconds to get hot water.
  • Almost no water goes to waste since you don’t have to flush gallons of cold water down the drain.

How does a recirculation pump work? Most use a sensor to measure water temperature near the heater or at a certain fixture. The pump activates as soon as the water temp has dropped below a certain threshold.

How can the water circle back? There are two options:

  1. Your home already has a recirculation line (dedicated return line) or you install one which is rather costly.
  2. You install a cross-over valve preferably at the farthest fixture from your heater. This one-way check valve connects the hot to the cold water line. It opens and closes based on water temp. This way the cold water can flow back to the heater through the cold water line.

Now, you might be thinking: “A recirculation pump in combination with a tankless water heater would cause a huge waste of energy due to frequent pumping and re-heating.” And you were right, if you wouldn’t make use of some type of smart control.

A smart control – this can be a timer, a button, a motion sensor, a remote… – ensures that the pump activates at certain times of the day only, let’s say right before you wake up in the morning.

Laing Recirculation pump

Laing Recirculation Pump with Timer & Thermostat – Available on

Another aspect to consider is pump volume. Too small of a pump with too little flow would fail to activate the water heater.

If you are interested to learn more, you can check out this pump that has a built-in timer + thermostat or this model that can be fired up with the help of a remote.

If you have any questions about how to install a tankless electric water heater please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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Leave a Comment:

Catrina says June 22, 2021

I am wanting to install for the shower only, do I wire it on the same line as the (electric jets) tub?

    Gene says September 8, 2021

    Sorry Catrina, it’s not possible to provide a useful answer without further details.

James Harvey says October 25, 2021

Your information is very helpful. Thank you for writing this!

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