How To Install A Water Heater Expansion Tank - Tommie's Plumbing (2025)

An expansion tank for your water heater helps relieve excess pressure in your plumbing system by absorbing any additional water produced from it. The tank should be connected directly to the cold water line that leads to your hot water heater for best results. This project can be considered moderately complex; however, most experienced home improvement enthusiasts should be able to complete it in the afternoon. Here are detailed steps to install a water heater expansion tank.

Why Are Water Heater Expansion Tanks Important?

As water expands, it creates extra pressure in your plumbing pipes, creating additional strain. A water heater expansion tank absorbs this extra stress to protect pipes and prevent damage by taking in all that extra pressure and dispersing it to avoid potentially devastating consequences for them.

Water heaters should be maintained because expansion tanks are essential safety devices that help relieve pressure in plumbing systems. Heating water generates thermal expansion, which creates extra pressure that needs somewhere to go; an expansion tank serves as an overflow space to handle this excess volume, preventing excessive pressure from damaging pipes or the water heater itself.

Water heater expansion tanks should typically be included when building or adding new plumbing to an existing water heater, although retrofit projects allow you to add one. If you lack experience in plumbing projects, professional water heater installation should generally be chosen to ensure this device’s proper function and safety.

Step 1: Spare Enough Space & Room

Step one in installing an expansion tank is finding enough room. Typically, this involves swapping out copper flex lines with longer or shorter ones and installing additional elbows and threaded adapters on cold water pipes – something a professional plumber should be able to assist with for an additional fee.

As your water heater heats up, thermal expansion occurs, and without an expansion tank, this could create excess pressure in your plumbing system, damaging valves, and supply pipes. An expansion tank helps alleviate this pressure by storing extra water until needed, thus relieving this excess stress on valves and pipes.

Step 2: Connect the Tee Fitting

Once all the pipes are connected, you can install the expansion tank. A tee fitting should be mounted about a foot above your water heater, with its bottom in contact with a dielectric union adapter. After that, a short piece of copper pipe should be attached directly to it using pipe-sealing tape for increased leak protection and to decrease the risk of overtightening, which could potentially damage the pipe and fittings.

Next, connect the top outlet on the tee-fitting to your municipal water supply pipe using short copper piping with push-fit or sweat-solder connections, preferably flexible piping that allows easy removal if an expansion tank needs replacing.

Step 3: Connect the Horizontal Pipe

Installing an expansion tank involves connecting it to the cold water line directly into your water heater. First, connect a short length of copper pipe fitted with a tee fitting directly onto the dielectric union adapter on the water heater—approximately one foot above. Use sweat-soldering or push-fit connections to join this connection between the tee fitting and copper pipe together.

Utilize a pipe wrench or channel-lock pliers to securely fasten a threaded copper expansion tank adapter onto the short piece of horizontal copper pipe you connected in Step 2. Use pipe-sealing tape as necessary to ensure it doesn’t overtighten itself.

Connect the top outlet of the expansion tank’s tee-fitting to the cold-water supply pipe using either copper flex line or rigid pipes (if applicable). Make sure to connect all hot-water pipe connections before switching on your water.

Step 4: Connect the Threaded Fitting

Locate and secure the threaded fitting on the expansion water heater tank by applying pipe sealing tape before fastening it securely with threaded adapters on horizontal pipes. Don’t over-tighten it, as this may damage pipes and fittings.

Once connected, use any suitable pipe type—however, many plumbers prefer copper flex lines. Once your tank has been connected to its mounting bracket and linked to your cold water source, lock its top outlet tee-fitting with it if possible. This allows easy use in case alternative uses become necessary in the future.

Step 5: Connect the Top Outlet

As water heaters expand, their increased pressure can place additional stress on plumbing fixtures and pipes in your home. A water heater expansion tank relieves these additional forces without endangering pipes or the tank itself by absorbing excess pressure when water expands.

Though you can install one yourself, a professional should handle the water heater installation for a little cost for the best results. This project requires close attention to detail, such as adjusting the lengths of copper flex lines and fitting sizes, before proceeding with this task.

Switch off your hot water breaker and, if applicable, any gas supply to a gas water heater before turning any hot water faucet on to drain any pressure out of the system and disconnect it.

Connect a tee-fitting to the short nipple of your water heater about one foot above, about one foot taller than it. This will provide clearance for an expansion tank. Use sweat-soldering or push-fit connections to join its top outlet to the cold water pipe. Most plumbers use copper flex lines; however, rigid pipes may also work.

Pipe-sealing tape should be wrapped around the threaded fitting on an expansion tank before attaching it to a threaded adapter on a tee fitting. Be wary of over-tightening, as that can damage both threads and fittings.

Conclusion

Installing a water heater expansion tank is a practical project that can protect your plumbing system from thermal expansion stresses. Proper water heater installation not only extends the lifespan of your water heater but also enhances the overall safety and efficiency of your home’s plumbing system.

Best Water Heater Installation by Tommie’s Plumbing

At Tommie’s Plumbing, we understand the importance of a well-installed water heating system and how its warranty can affect the overall longevity. With our expertise and dedication to quality service, we offer various services, including water heater installation, tankless water heaters, sewer and drain cleaning, assistance with high water bills, and fixing high water pressure issues. Contact Tommie’s Plumbing today for reliable solutions tailored to your needs.

How To Install A Water Heater Expansion Tank - Tommie's Plumbing (2025)

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