How to Install or Replace a Tankless Water Heater

Step 1

Read the Product Manual Thoroughly

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

Step 2

Pull Permits

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

Step 3

Be Sure You Have the Right Water Pressure

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 “Establish the cold and hot water connections” section below).

Step 4

Choose a Location for Your Tankless Gas Water Heater

• Check your local building code to confirm where you can install your water heater within your home.
• These tankless gas units need to vent directly to the outside through a pipe, not through a chimney. It’s necessary to find a spot that will let the unit vent outside easily, while following local code for vent location.
• Read the manufacturer’s installation instructions carefully to make sure you have enough clearance around the unit.
• 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.

Step 5

Measure the Install Space

Carefully measure the space where you want to place the water heater, so you purchase the right-sized unit.

Step 6

Verify or Upgrade your Gas Line

• Tankless gas water heaters use more gas than tank style ones. So, first determine whether or not your current gas line will suffice.
• If your current gas line won’t cut it, you’ll need to get a licensed contractor to install a newer, bigger gas pipe.

Step 7

Remove Your Old Water Heater

• 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.

Step 8

Mount the Unit

• Create a mounting box that will securely support the unit, and mount it about four inches out from the wall. Use proper anchors for the foundation wall. 
• Follow the manufacturer’s directions to securely mount the unit to the box.

Step 9

Install the Gas Line

• Unless you have strong experience with gas pipe connections, hire a licensed contractor.
• If your current gas line is the appropriate size and you can connect to the existing tee, use a threaded black iron pipe to continue the gas line to the unit location. If you’re removing the down pipe for the old unit, remember to turn off the main gas line beforehand. 
• After you make sure the gas line runs to the proper place, install a tee, sediment trap, and gas shut-off valve. Follow the manufacturer’s instructions to connect the shutoff valve and sediment trap to the heater.
• Run a new gas supply line from the tee to a spot where it can easily attach to the new unit’s gas line. You can use a black pipe or flexible gas supply line.
• Use two wrenches to assemble the connections towards the heater, starting at the tee. Use thread sealant designed for gas lines when making gas pipe connections.
• After you finish making all the gas line connections, test the line. Use a gas pressure test gauge before turning on the gas.

Step 10

Install New Water Lines

• Follow the manufacturer’s directions to connect the water heater valves to the water supply line.
  • Use copper pipe to connect new hot and cold water lines to existing water lines.
  • Run the lines to the new unit. You may need to cut and solder copper piping to the unit.
• You may need an expansion tank near the cold intake if your water system has an anti-siphon valve or check valve on the supply line. Refer to your owner’s manual for more information.
• Secure the pipe against the wall with bell hangers.
• Install the pressure relief valve. Follow the manufacturer’s directions for installing a purge valve and pressure relief valve.

Step 11

Check for Leaks

• Turn on the water supply and check for leaks.
• Turn on the gas and check for leaks. You may need to bleed the line.
• Then, turn the gas line off until the installation is complete.

Step 12

Install the Exhaust Vent

• Use the manufacturer’s instructions as a guide for venting the unit properly. There’s a good chance that you can vent the water heater directly through your home’s rim joist. Only use pipes that are rated for this type of venting. You’ll need a vent kit, depending on the manufacturer. 
• Apply heat-resistant silicone sealant to the vent shaft of the new unit. Then, place a connector on it and secure it with a hose clamp.
• Place a section of stainless steel vent pipe on top. 
• Slip on a retaining ring. Secure it by folding over the tabs.
• Slip on an elbow. Point the opening in the direction where the unit will vent to the outside. 
• Choose a point on the joist or wall to be the center of the vent hole for venting outside. At the chosen spot, drill a hole from the inside
• Use a vent thimble to outline a circle on the outside wall. Near the top of the circle, bore a 1-inch hole, using a spade bit. Use a reciprocating saw to cut out the vent hole. 
• To allow the flange thimble to be flush against the outside wall, remove siding and shingles from around the vent hole. 
• Place silicone caulk around the edge of the flange. Then, insert the flange into the vent hole. Use screws to secure it well to the outside wall and seal them with silicone. 
• From the inside, install the interior flange.
• Run a section of vent pipe through the flange opening. Secure each section with the tabs.
• From outside, connect a small section of vent pipe and connect the vent hood.
• Put back the shingles and siding you took off earlier.

Step 13

Purge Air from Water Pipes

• To purge air from the water pipes and heater, open a faucet to full “hot.” 
• Turn off the faucet.

Step 14

Plug in the Water Heater

Plug in the water heater. It’s that simple.

Step 15

Insulate Hot Water Pipes

Insulate the hot water pipe that comes from the water heater.

Step 16

Turn on the Gas

After installation is complete, turn on the gas. Your water heater should now be functioning!

Step 1

Read the Product Manual Thoroughly

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

Step 2

Confirm Sizing of Your Electrical Service Panel

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.

Step 3

Be Sure You Have the Right Water Pressure

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 “Establish the cold and hot water connections” section below).

Step 4

Pull Permits

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

Step 5

Find the Perfect Spot

• 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.

Step 6

Turn Off Circuit Breakers

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

Step 7

Turn off the Main Water Supply

You don’t want to flood your workspace!

Step 8

If Needed, Disconnect Your Existing Water Heater

• 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.

Step 9

Take Off the Cover

• 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.

Step 10

Mount the Unit to the Wall

Its package should include the appropriate anchors and screws. 

Step 11

Establish the Water connections

• 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.

Step 12

Purge Air & Check For Leaks

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

Step 13

Close the Water Outlets

Do not skip this step!

Step 14

Create the Electrical Connections

• 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.

Step 15

Put the Cover Back On

Use the screws you removed earlier.

Step 16

Turn on the Circuit Breakers

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

Step 17

Check the Water Temperature

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.