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How To Install a Tankless Water Heater

For many people tankless water heaters provide a suitable alternative to the traditional storage tank type water heater. Tankless water heaters only use energy to heat water when you open a hot water tap thus saving money on your energy bill. This depends, of course, on how you utilize your tankless water heater. Misuse of the unit, e.g. taking extra long showers, can cost you as much in energy as your old tank type unit. Installing a tankless water heater is usually a job for a professional but the competent do-it-yourselfer can accomplish the installation with a minimum of problems.


Used properly, a tankless water heater can save you incredible amounts on your utility bill

Used properly, a tankless water heater can save you incredible amounts on your utility bill

  1. Determine your hot water consumption. The more hot water you use, the more you stand to save on your energy bill with a tankless water heater. Calculate how many hot water loads of laundry you do daily as well as how many hot showers everyone in your household takes. Include the number of automatic dishwasher loads you do every day as well. The manufacturer of your appliances can tell you how much hot water they use per load.
  2. Determine whether you will purchase and install an electric tankless model or a gas unit. If you opt to install a gas unit, make certain that you purchase the tankless unit equipped for the gas your utility provides you. Natural gas and propane are not interchangeable.
  3. Check out the proposed location for your water heater. Tankless units are designed for either inside locations or outside locations. Make sure you purchase a unit designed for an outside installation and that it is freeze protected according to the manufacturer’s instructions.

Installation of the tankless water heater

  1. Route a hot and cold water line to the water heater location.
  2. For a gas installation, install the proper gas line sized for your water heater to the water heater location. Make sure to test the new gas pipe installation for leaks before hooking it up to the gas valve on the unit. Verify that the new gas line is properly sized for the water heater as well as all the other gas appliances in your home.
  3. For an electric tankless water heater, install the proper size electrical cable to the unit location according to the NEC. Make certain that you have installed the proper size circuit breakers in your electrical panel to accommodate the water heater. In some cases, you may have to upgrade your electrical panel to accommodate the new breakers.
  4. Once you have the water, gas, or electrical installed, hang the tankless water heater on the wall and vent it for gas. Usually tankless water heaters will require a minimum of a 5″ B vent extended above the roof at least 5 feet above the highest point.
  5. If you are going to use a remote thermostat route the thermostat wire now to the thermostat location.
  6. Install the temperature and pressure relief valve in the unit and pipe it to an exterior location without using valves, caps, or plugs.
  7. With the gas or electricity off, flush water through the unit until it flows clear.
  8. Turn on the electricity and/or gas and open up a hot water faucet in the home. Hot water should appear at the faucet within a couple of seconds depending on how far the water heater is located from the faucet and how much water pressure you have.
  9. Adjust your thermostat for the temperature you want and you are ready to go.


There is limited space in the bottom of some tankless water heater models so make sure you plan your installation to use a minimum number of fittings.

Verify that your installation complies with all applicable codes and the manufacturer’s installation instructions.

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