DIY Network

Installing a Tankless Water Heater

Looking for a way to save energy? Get rid of your old hot water heater and replace it with a tankless one.

More in Plumbing

  • Time

    Under Half Day

  • Price Range

    $500 - $1,000

  • Difficulty



Step 1: Run a Vent Pipe

If replacing an old hot water heater with a new tankless hot water heater, using the same location will minimize extra steps (vent pipe, water pipe and gas line extensions). If installing for new construction, find a location near an exterior wall to run a vent pipe. A vent pipe must run from the tankless hot water heater to an outside location and must be vented downward to prevent elements such as rain water from entering the pipe (Images 1 and 2). Vent pipes can range in diameter. If an existing vent pipe does not meet the proper dimensions of the new tankless hot water heater, a new pipe will need to be run. Note: Some models require a separate pipe for fresh air intake. These models will call for additional thimbles and thimble holes.

Step 2: Cut Holes

To install a new vent pipe, measure the interior and exterior walls for thimble holes. Cut holes using a saw (Images 1 and 2). Test thimble but DO NOT install thimble until vents have been installed and angles have been checked. Once thimbles have been installed, slide the vent pipe into thimble securely. Note: Make sure to consult the directions of the specific tank model for local and national code requirements.

Step 3: Mount the Heater

Once the new vent piping has been completed, it's time to mount the tankless hot water heater. Make sure the tank lines up with the vent pipe(s). Note: If installing in a concrete or brick basement you will need to attach 2x4s to a joist (a wooden support beam that runs along the ceiling), in order to attach a backboard. Measure the backboard to the precise dimensions and attach to the 2x4s. Line up the tankless hot water heater with the vent pipe(s) and screw it into place.

Step 4: Attach Water Pipes

New water pipes must be run to supply the tankless hot water heater with water. When attaching new copper water pipes, the ends of each pipe must be cleaned with an emery cloth. Next apply soldering flux to the end of the pipe and slide the pipe into the fitting. Apply the heating torch to the fitting with the inner flame tip for about 10 seconds. Once the metal is hot enough it is time to apply the solder. Touch the solder to the joint and work your way around the fitting on both sides until the joint fits. Note: A separate isolation valve kit allows for easier maintenance and a relief valve prevents pressure build-up. Note: Tankless hot water heaters can be electric or gas. For gas tankless hot water heaters, a T valve must be installed to an existing gas line. Once a T valve is installed, a corrugated stainless steel gas line must be run from the valve to the tankless hot water heater. A gas shut off valve must be attached to the line before connecting to the sediment trap (the short section of pipe running downward on the bottom of the tank). Once properly attached, use a sensitive gas sniffer to detect any gas leaks.