How to Install a Water Heater Expansion Tank detailed guide

Learn how to install a water heater expansion tank with our step-by-step guide. Ensure the proper functioning and longevity of your water heating system.


Installing a water heater expansion tank is a crucial step in maintaining the efficiency and longevity of your water heating system. This detailed installation guide will help you with a step-by-step guide on installing a water heater expansion tank. We’ll cover everything from gathering the necessary tools and materials to the installation process. Following these instructions ensures a smooth and successful installation, allowing your water heater to operate optimally.

Before we dive into the installation process, let’s briefly understand the purpose and benefits of a water heater expansion tank.

Understanding the Purpose of a Water Heater Expansion Tank:

A water heater expansion tank is designed to alleviate excess pressure within a closed plumbing system. When water is heated, it expands, which can cause an increase in pressure. Without an expansion tank, this pressure can stress the water heater, pipes, and fixtures, potentially leading to leaks or damage. The expansion tank acts as a safety valve, absorbing the expanded water and reducing the strain on the system.

expansion tanks for water heaters

Step-by-step thermal expansion tank Installation process

Step 1: Gather the Required Tools and Materials:

Before starting the installation, make sure you have the following tools and materials:

  • Water heater expansion tank (properly sized for your system)
  • Pipe wrench or adjustable wrench
  • Teflon tape or pipe joint compound
  • Pipe cutter or hacksaw
  • Fittings and connectors (if necessary)
  • Safety goggles and gloves
  • Towels or rags
  • Bucket or container to catch any water

Step 2: Choose the Right Location for the Expansion Tank:

The expansion tank should be installed on the cold water supply line, preferably near the water heater. Choose a location that allows easy access and sufficient clearance for future maintenance.

Step 3: Shut Off the Water Supply and Drain the System:

Turn off the main water supply to your home. Next, open a hot water faucet to relieve any pressure in the system. Attach a hose to the water heater’s drain valve and drain the tank into a suitable container or drain.

Step 4: Install the Expansion Tank:

steps showing how to install an expansion tank on water heater


The above image shows steps to install expansion tank on tankless water heater and they are explained in detail below.

A) Attach the Dielectric Union

  • After positioning the water heater correctly, locate the cold water entry port.
  • To prevent leaks, wrap the threads of the dielectric union with pipe-sealing tape.
  • Using a pipe wrench or channel-lock pliers, thread the dielectric union into the cold water inlet port on the water heater, ensuring a secure connection.

B) Connect the Copper Adapter and T Fitting

Copper adapter pipe

  • Wrap several loops of pipe-sealing tape around the top threads of the dielectric union.
  • Thread a female threaded copper adapter onto the union, ensuring a tight and secure fit.
  • Use a pipe wrench or channel-lock pliers to tighten the copper adapter securely, preventing any potential leaks.

T Fitting

  • Connect a short length of copper pipe and a tee fitting to the adapter on the water heater’s dielectric union.
  • Position the tee fitting approximately one foot above the water heater to allow sufficient clearance for the expansion tank.
  • Most plumbers prefer sweat-soldering for these connections, but push-fit connections (such as “shark-bite“) can also be used.

C) Attach copeer pipe to T with L fitting

Connect a copper pipe to the T fitting, its length should be the expected distance of the expansion tank from the water heater, keep it little away from water heater as it could provide litle free space during maintainace.

Step 5: Connect the Expansion Tank

a) Use Teflon tape or pipe joint compound on the threads of any fittings or connectors required to connect the expansion tank.

b) Ensure secure connections using a pipe wrench or adjustable wrench. Do not over tight them, doing so could damage the treads which further cause leaks.

c) Double-check all connections to ensure there are no leaks.

Step 6: Reopen the Water Supply and Check for Leaks:

Gradually turn the main water supply on and allow the tank to fill. Keep an eye out for any leaks around the expansion tank and its connections. If leaks are detected, tighten the fittings or connectors as needed.

Step 7: Test the System:

Once the tank is filled and there are no leaks, close the hot water faucet previously opened to relieve pressure. Check the water heater and other fixtures for proper operation and ensure the pressure relief valve functions correctly.

Step 8: Final Steps and Maintenance:

Clean up any spills or water residue and dispose of the drained water properly. Keep an eye on the expansion tank periodically to ensure it continues to operate effectively. Consult the manufacturer’s instructions for any specific maintenance requirements.

Safety precautions to follow during the installation process

Several safety precautions should be followed during the installation process of a water heater expansion tank. These precautions help ensure the safety of both the installer and the proper functioning of the water heating system. Here are some important safety guidelines to keep in mind:

Turn off the Power and Gas: Before beginning any work, turn off the power supply and Gas to the water heater at the circuit breaker and Gas supply connection. Doing so will prevent electrical accidents, shocks or gas leaks while working on the system.

Shut off the Water Supply: Close the main water supply valve to the house or building. Doing so will prevent water from flowing into the system and minimize the risk of flooding or accidental water discharge during the installation.

Drain the Water Heater: Open a hot water faucet in your home to relieve pressure in the water heater. Next, attach a hose to the water heater’s drain valve and drain the tank into a suitable container or drain. Doing so will remove any remaining hot water and reduce the risk of scalding or burns during the installation.

Use Proper Tools and Equipment: Ensure you have the necessary tools and equipment for the installation, such as pipe wrenches, adjustable wrenches, safety goggles, gloves, and a pipe cutter or hacksaw. Using the right tools for the job will minimize the risk of accidents and injuries.

Follow Manufacturer’s Instructions: Carefully read and follow the manufacturer’s instructions for the specific water heater expansion tank you are installing. Each manufacturer may have specific guidelines and safety precautions unique to their product. Adhering to these instructions will help ensure a safe and successful installation.

Check for Gas Leaks ( for Gas Water Heaters): If you have a gas water heater, it is important to check for gas leaks before and after the installation. Use a soapy water or gas leak detection solution to check for leaks around the gas connections. If you detect a gas leak, immediately turn off the gas supply and contact a professional plumber.

Inspect for Water Leaks: After the installation, carefully inspect all connections and fittings for any signs of water leaks. Look for drips or wet spots around the expansion tank and its connections. If you notice any leaks, tighten the connections or seek professional assistance to ensure a proper seal.

Dispose of Waste Properly: Dispose of any waste materials, such as old fittings or packaging, in a responsible and environmentally friendly manner. Follow local regulations and guidelines for the proper disposal of waste materials.

Frequently asked Questions

Q: What is the recommended size of an expansion tank for my water heater?

A: The recommended size of an expansion tank for water heaters in the range of 40 to 50 gallons is typically a 2-gallon expansion tank.

Q: How much does an expansion tank cost?

A: The cost of an expansion tank can vary, ranging from around $40 to $200 or more, depending on the size required for your specific water heater. Factors such as brand, quality, and additional features can also influence the price.

Q: Do tankless water heaters need expansion tanks?

A: This needs a clear explaination, so, refer tankless water heater expansion tank article.

Q:What side does the expansion tank go on a water heater?

A: The expansion tank for a water heater is typically installed on the cold water supply line, near the water heater itself. It is commonly positioned after the shut-off valve and before the water enters the water heater. This location allows the expansion tank to effectively relieve excess pressure and accommodate the expansion of water as it heats up.

Q: Can I install a water heater expansion tank myself, or should I hire a professional?

A: While it is possible to install a water heater expansion tank yourself, it is recommended to consult a professional plumber if you are unsure or uncomfortable with the process.

TanklessHelp Staff

TanklessHelp Staff has an experienced writers and researchers in the field of water heating technology. With a background in HVAC and plumbing, Tanklesshelp staff has in-depth knowledge in many types of waterheaters in America and Canada. They have a passion for educating homeowners and businesses on solving easy to hard repairs and guide them on how to maintain them to save money.

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