DIY Network

How to Install a Tankless Water Heater

Tankless water heaters save space and energy. Paul Ryan gives step-by-step instructions on how to install a tankless hot water heater.

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tankless water heaters save space and energy
  • Time


  • Price Range

    $2,500 - $5,000

  • Difficulty



Step 1: Measure, Cut and Polish the Pipe

Measure your copper pipe to fit, and then cut it with a rotating pipe cutter (Image 1).

A 120-grit emery cloth will take the burr off the end of the pipe and a wire brush polishes the inside of the fitting (Image 2). You need bright shiny copper on both surfaces to ensure a good tight joint.

Apply flux on the pipe and fitting.

Step 2: Secure the Pipe Clip

Dry fit your copper pipe to make sure it all fits in place and mark the place for a pipe clip to hold the pipe in place.
Pre-drill holes for the expansion anchors and secure the pipe clip in place (Image 1).

Tip: Remember to dry fit components before soldering.
Note: It is hard to believe that the small unit of the tankless water heater will heat water like a traditional water heater. However, a traditional water heater has two heating elements and the tankless has four. Because water travels through at close proximity, it instantly heats the water. This uses more energy than a regular heater, but it only uses the energy while it's on -- unlike a traditional tank that uses it during a 10 minute shower and then has to reheat the cold water coming in.

The system uses a flow switch that was designed by NASA. The flow switch alerts the system that hot water has been demanded. The microprocessor sends a signal to the heating elements to produce hot water, consuming energy only when a hot water tap is being used (Image 2).

Step 3: Sweat the Joints

Sweat the plumbing joints before putting the new hot water heater to work.

Expert Tip: When sweating soldering copper, heat the fitting -- not the joint. The heat will draw the solder to it.

sweat plumbing joints

Step 4: Install the Disconnect Panel

Once you sweat the joints, an electrician can install the disconnect panel by the water heater. You may need to upgrade your entire electrical service. The water heater alone requires a 100 AMP service to heat the water so quickly, so the house needs to have a minimum of a 200 AMP service. The upgrade will include changing the mast meter housing on the outside of the house.

Expert Tip: It is important to remember that any heating appliance exceeding 48 amps must be supplied with a disconnect service panel and a breaker by the manufacturer based on a UL requirement in the National Electrical Codes.

You need to run water through the unit before powering it up. Let the water run for two minutes to void damage to the unit. It may take a little trial and error to adjust the thermostat to get the water at a comfortable setting.

Step 5: Insulate the Pipes

Insulating your pipes will do two things: it will keep the hot water hot in the hot pipes and it will reduce the condensation in the cold pipes during the summer. Reducing condensation reduces the humidity.

The pipe insulation is approximately $2 a piece and is pre-slit to make it easier to fit over your pipes.

Hold up the insulation to see how long the pipes are and then cut it to length. Miter the ends at a 45 degree angle to fit on the corners, then slip the insulation onto the pipes.