How to Install or Replace an Electric Tankless Water Heater

Some manufacturers will void the warranty if their systems aren’t installed by licensed contractors.

Confirm whether or not your electrical service panel can handle the energy needs of an electric tankless water heater. You might need to upgrade your panel or run a brand new one.

To find relevant information, you can look at the electrical breaker box or label in your electrical panel. You can also ask an electrician.

Most sufficient water heaters require a minimum of four 40AMP breakers to supply hot water for a 2 1/2 bath home.

If incoming water pressure is above 80 psi, you’ll need to install a pressure reducing valve upstream of the new water heater. If you need to install one, you should do that when installing the cold and hot water connections (see Step 11 : Establish the Water Connections below).

Make sure you pull any required state or city permits for installing or replacing a water heater. 

• For heating water for the entire home, you’ll want to place the unit closest to where most of the hot water is used.
• For a point of use system, place these as close to the points of usage as possible.
• Keep in mind that most electric tankless water heaters have to be installed vertically, with water and power supply connections facing down. 
• Follow manufacturer’s directions on leaving at least a certain minimum clearance for servicing.
• Overall, you want to avoid areas where: 
  • Freezing temps can affect the unit.
  • Any type of liquid could regularly splash on the unit.
  • There’s a lot of humidity and moisture.

Turn off all circuit breakers related to the new unit. This is very important!

You don’t want to flood your workspace!

• Turn off the water supply to the unit. 
  • If there’s no shut off valve before the heater, turn off your main water supply.
  • Shut off any power and gas supply valves feeding the heater.
  • Drain the unit. 
    • For hot water, use a hose rated to withstand heat. Open a hot water faucet to release pressure in the system. Let it fully drain. 
• Disconnect the water heater from the gas and water lines. 
• Dispose of your old water heater properly. 
  • Contact your local recycling and/or sanitation departments for information on how to properly get rid of it.

• Remove any screws that are securing the front cover of the new unit. 
• Important: You might have to remove at least one plug before you can put it aside.

Its package should include the appropriate anchors and screws. 

• Establish the cold and hot water connections. Cold is usually on the right side.
  • The easiest route is using stainless steel flex pipe with Teflon tape.
  • You can also use copper tubing that’s rated for high temperature applications. 
  • If you need to cut into a pipe, clean up the edges. 
  • When you solder pipes, flush them before connecting them to the water heater. And remember that excess heat can damage the water heater.
  • It’s a good idea to install a shut-off valve before and after the heater, to turn off the water supply to the unit for maintenance without shutting off the supply to the rest of your home.
  • If you need to install a pressure reduction valve, you should do so now on the cold water side. 
  • You probably won’t need to install a temperature and pressure relief valve (T&P). But, you should confirm whether or not you need one, by checking your local and state installation codes.

• Purge air from the unit and the pipes by opening several hot water outlets. 
• While waiting, you should check every connection for any leaks.

Do not skip this step!

• The heater should be on one side and the electrical panel on the other. 
• Follow the manufacturer’s wiring diagram, and their directions for choosing the correct wire, circuit breaker number, and circuit breaker size. 
• After cutting every wire set to length and stripping it, push them through the bottom holes of the new water heater’s housing.
• Then secure the wires to the right slots on the terminal block.
  • Refer to the product manual for optimal torque.
  • Remember that for each circuit, a ground conductor needs to be connected to the circuit breaker panel and the unit’s grounding busbar.
• Check all of the electrical connections, to confirm that you placed all the wire sets correctly.

Use the screws you removed earlier.

Now, the unit should be on. Choose your preferred unit settings.

Turn on the hot side of a faucet in your home. Check the water temperature after it has stabilized. If you want to adjust the temperature, adjust it on the unit.