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How to Install an Expansion Tank for Your Hot Water Heater

Traditional water heaters store water in a tank, but as it is heated, water expands. This can put extreme pressure on your plumbing system. An expansion tank holds excess water to relieve pressure and prevent damage to valves and plumbing fixtures. Here, we’ll look at how it works and how to install an expansion tank in your home.


Do I Need an Expansion Tank?


You may need one attached to your water heater if:

  • Water drips from the relief valve or plumbing fixtures are rapidly deteriorating.
  • Applying for a water heater permit requires installing an expansion tank.
  • The system has a limiting valve or back-flow system.

The expansion tank in a closed plumbing system provides space for water, which can increase in volume by 2% when heated from 50 to 120℉. There are two sections in the tank, divided by a rubber diaphragm. One section accepts water undergoing thermal expansion. The other is an air chamber that pressurizes as the diaphragm expands.


Installation Process

Before you install an expansion tank, find one that’s the best size for your water heater and plumbing system. You may not need a plumber for the installation. A common size is 2 gallons. A ¾ threaded connection is needed to secure the tank and a tee fitting above the water heater will help secure it. To install the tank:

  1. Disconnect Water and Power: Stop the water flow via the shut-off valve on your supply line. For electric hot water heaters, turn the power off at the breaker; the gas supply must be switched off for a gas-powered unit.
  2. Verify Where the Cold-Water Supply Line Is: Find the cold-water line that is horizontal to the water heater, which is where you will make the connection for the expansion tank.
  3. Dielectric Union: This connects directly to the cold-water entry port. Use pipe-sealing tape to wrap the threads, and thread the union into the port on the water heater. Channel-lock pliers or a pipe wrench will be needed to tighten it.
  4. Attach a Copper Adapter: Loop the pipe-sealing tape around the union’s bottom threads several times. Next, thread a female threaded copper adapter onto the union and tighten the adapter with pliers or a pipe wrench.
  5. Connect the Tee Fitting: This fitting is placed atop a short length of copper pipe that’s installed on the water heater. To provide sufficient clearance for the tank, install the tee-fitting about one foot above the appliance. The connection can be made via sweat-soldering or with push-fit connections.
  6. Install the Tank: Wrap plumber’s tape around the bottom of the tank’s connector. Then place a tee fitting on the connector and tighten it with a wrench (there’s usually a ½ or ¾ inch threaded fitting on the tank to join it with the cold-water supply). Don’t over tighten the connector as this can damage it. A short length of threaded or sweat-soldered pipe may be needed as well.

Next, connect the tee-fitting’s top outlet to the cold-water supply pipe. Sometimes, this is accomplished using a copper flex line. Nonetheless, rigid pipes can be used where applicable. Connect hot-water pipes as well before turning the water heater back on. You can now open the water valves and test the system.

Expansion tanks are usually installed directly above the water heater in a vertical position; if space is limited, you can install it horizontally. A saddle fitting is typically included, so you can install the tank without using heat or special tools.


Request Help from Village Plumbing

We are a Houston plumbing company that provides all types of hot water heater services and can assist if you aren’t sure how to install an expansion tank. Our team specializes in water heater repair and maintenance, including flushing sediment and performing routine inspections. To schedule service, call 713-526-1491 today!

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