Tip

The instructions below use existing copper tubing, and should be taken as general guidance.

It typically sits vertically but can also sit horizontally if there are space constraints and your specific tank allows.

Tighten Adapter

Tighten the copper adapter securely with a pipe wrench or channel-lock pliers.

Expansion tank installed over water heater with copper pipe

The Spruce / Kevin Norris

Next, attach a female threaded adapter to the horizontal pipe using your preferred connection method.

Many plumbers opt to make this connection with a copper flex line instead of a rigid pipe.

This can cause damage, stress, leaks, and even bursting pipes.

Materials and tools into install a water heater expansion tank

The Spruce / Kevin Norris

If maintained properly, a water heater expansion tank can last five to 10 years.

Water supply turned off lever turned on main shut-off valve

The Spruce / Kevin Norris

Dielectric union wrapped with pipe-sealing tape on cold water entry port

The Spruce / Kevin Norris

Copper adapter threaded on dielectric union

The Spruce / Kevin Norris

Channel-lock pliers tightening dielectric union to adaptor

The Spruce / Kevin Norris

Copper pipe and tee-fitting attached to water heater’s dielectric union adaptor

The Spruce / Kevin Norris

Short copper expansion tank pipe attached to tee-fitting

The Spruce / Kevin Norris

Expansion tank attached to adaptor on horizontal pipe

The Spruce / Kevin Norris

Copper flex line connected to top outlet of cold water supply pipe

The Spruce / Kevin Norris