How to Install a Water Heater Expansion Tank

The first step is turning off the water supply to your home! Turn off your hot water heater next. You should also open the lowermost faucets in your home to drain pressure from your water line.

Think of the dielectric union as the translator between your water heater and expansion tank. This special adaptor is used to isolate the connections of dissimilar metals. With your water heater in the correct position, attach a dielectric union to its cold-water entry port. Next, use pipe-sealing tape to wrap the dielectric union's threads. The union can then be threaded into the cold-water inlet port on your water heater using pliers or a pipe wrench.

Carefully wrap a series of loops of pipe-sealing tape over the top threads of your dielectric union. Next, thread a female threaded copper adapter over the union. The last part of this step is tightening the copper adapter securely using your wrench or pliers.

Also known as a pipe tee, a tee fitting is a T-shaped pipe with two outlets that connect to the main line. The purpose of the tee fitting is to connect piping with a right angle linearly. To attach a tee fitting, install a short length of copper pipe and your tee fitting to the adapter on the dielectric union located on the water heater. When installing piping, you have the choice to either use the sweat-soldering method that involves a propane torch or purchase plastic or copper fittings offering push-fit connections.

Attach a short length of copper piping to the outlet on the tee fitting you just installed. When selecting your copper length, you'll need to improvise based on how much space is available. However, it's recommended to avoid going longer than 6 inches. The next part of this step is attaching a female threaded adapter. You again have the choice to either use the sweat-soldering method or push-fit connections.

Locate the threaded fitting on your expansion tank. Next, wrap pipe-sealing tape around the fitting. Carefully screw the fitting into the threaded adapter that is located on the unit's horizontal pipe. Be careful about over-tightening when screwing the fitting in place. While tighter is often better in most things related to home DIY, this is one case where you can easily damage pipes and fittings by being too aggressive.

In this "almost final step" for how to install a water heater expansion tank, connect the top outlet on the tee fitting to your cold-water supply pipe using your pipes and fittings. While you have the freedom to select the materials you want to use with this one, one pro tip is to use a flex line instead of a rigid line. Next, finish the connections between the hot water pipe and the water heater.

It's important to test your work before walking away. To do this, turn on the water heater. You'll then want to open the water valve that connects your home to its water supply to observe the unit's operation. Monitor the faucets that were opened to drain out at the start of the project. You can shut them once you observe a steady stream of water coming out from them. Finally, confirm that no leaks are occurring as the unit is operating. If you find that your water heater keeps tripping the breaker after your DIY installation, this is usually a sign that water is leaking onto electrical lines.