How To Install a Tankless Hot Water Heater

An Electric Tankless Heater Is an Easy DIY Project

One of thing I learned about tankless electric heaters is how easy they are to install. With a how-to book, a pipe cutter and a few basic tools, you should be able to make this a smooth project. I suggest first finding a good spot. Your hot water heater should be mounted where it will do the most good and is easy to get to.

Step 1


Start by turning off the water where it enters the house and open all faucets to drain the system. Decide where you are going to join into the old pipes by taping a fitting on an existing pipe and begin to work your way back to the new tank.

The easiest way to join pipes together is to use compression fittings. Simply cut pipes to length, clean ends to remove burrs and dirt, and press into a fitting with a twisting motion. I used flexi-pipe for the last segment to the heater. Be sure to install hot and cold cutoff valves near the heater. That’s it.

Step 2


The first thing is to throw the main breaker off. Next remove the panel cover and use a simple circuit tester to be sure there is no current before starting to work.

You should already have determined that your breaker box can handle the added amperage of this tankless unit and has enough slots for new breakers. For an 80-amp heater this will require two 40-amp breakers. For a 120-amp heater, it will require three 40-amp breakers. This is for a Bosch -- other models may be different. Each of these double breakers is wired to the heater with its own pair (plus ground wire) of copper wires. Be sure to use the recommended gauge of wire.

Step 3

Finish Wiring

Punch out slugs in panel where the new breakers will fit through and reinstall cover. Leave new breakers turned off for now. Next run these wires to the tankless heater. Connect wires to tankless heater terminals as shown in the installer’s guide that came with the heater.

Step 4

Almost finished

You are ready for a test run. To do this be sure that the tankless water heater breakers are off. Then turn on all the faucets in the house and open the valves at the tank. Remember to turn on your main water supply. This test run is to remove debris and prevent vapor lock. Check for leaks. If your tank didn’t come with a filter, a small mesh type can be installed at the cold water coupling later.

Step 5

Test run

Turn off all the faucets in the house but a shower nearest to the water heater. Throw the main and the breakers on. The red light should come on and you should have hot water in about 10 seconds.

Step 6


You have two adjustments - the heat dial and the inline hot water valve from the tank. Both temperature and water flow may have to be adjusted to fit your comfort level. Remember hotter water means lower flow rate.


  • Circuit tester
  • Screw driver
  • Pliers
  • 2 adjustable wrenches
  • Pipe cutter
  • Wire cutters
  • Electrical tape
  • White plumber’s tape
  • Green pot scrubber
  • Compression release tool

A final word

It is always smart to work safely when doing electrical work. Because breaker panels are all different, it is a good idea to have a how-to book that you can refer to.


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