How to Install a 40 Gallon Water Heater

Your old water heater, after years of faithful service, quit working and needs replacing. You have a 40-gallon water heater, which is a standard size for most homes. Installing a new water heater seems like a rather daunting task, but you actually can install a water heater yourself.

How to Install a 40-Gallon Water Heater

  1. Turn the power off to the water heater before working on it -- electricity and water do not play well together.

  2. Drain the water heater. Hook a hose to the drain at the bottom of the water heater and run it outside or to a floor drain, if one is near your water heater. (note the warnings listed at the end of this article.) Open the drain for the water heater all the way and make sure the water is flowing well through the hose. Then turn off the water to the water heater. Open the relief valve at the top of the water heater and turn on a couple of hot-water faucets in the house. This breaks the vacuum and allows the water to drain properly.

  3. Disconnect water lines. While the water heater is draining, disconnect the hot- and cold-water lines going in at the top of the water heater.

  4. Disconnect the electrical wires. Double-check to make sure you have turned off the power to your heater. Use your electrical tester on the top element to be certain the power is actually off. Disconnect the electrical wires at the top of the water heater.

  5. After the water heater has finished draining, remove it and replace it with your new water heater. You will reconnect your new water heater exactly like you disconnected your old water heater. Leave the power to the water heater off. Turn on the water, though. Leave at least one hot-water faucet on in the house until the water heater finishes filling. Check for leaks, then turn on the power to the water heater. In a short time, after the water has heated, you will be ready to use hot water normally.


  • Always make certain that the power is off to the water heater before touching any of the electrical wires. Do not run the drain hose into a bathtub, because water does not flow uphill. Be careful where you place the end of your drain hose, because the water coming out of your water heater will be hot. Hot water can kill flowers, plants, and grass. If you have problems, you should always call a licensed, professional plumber.