If you have bought a water heater expansion tank and are looking for how to install it? Then, we got you! In this article, we will provide you with a complete guide on the installation process of the expansion tank and tell you where it is best to install it.

The advised water pressure is 60 PSI for residential buildings. But the average pressure in U.S households is 80 PSI. A water heater expansion tank is essential to negate the threat of leakage due to high pressure.

A Complete Guide on Water Heater Expansion Tank Installation Process.

After doing complete research on water heater expansion units, we completed this task in 7 quick and easy steps. 

But first, have a look at the tools we use. The plumbing unit will depend on the types of expansion pipes and orientation of the water heater. 

Required Plumbing Equipment For Installation.

  • An Expansion Tank
  • Pipe Wrench
  • Dielectric Water Heater Union (For Copper Pipes) or Pipe Joints
  • Hacksaw
  • Drill Machine (You may need it later)
  • Pipe Sealing or Teflon Tape
  • Tee Fittings
  • Hand Pipe Thread
  • Screw

The Installation Process of Expansion Tank to Water Heater in 7 Easy Steps.

Once you gathered the required plumbing items. Follows these instructions;

  1. Disconnect the power and water supply.
  2. Bring out the expansion vessel with all accessories nearby the heater.
  3. Check the cold line.
  4. Install the water heater expansion tank by placing it on the hard water supply line.
  5. Attach the heater tank.
  6. Restore the power and water supply.
  7. Test Trial.

Step 1. Power and Water Disconnection.

Stop the water supply to the heater by switching off the valve attached to the supply line. Once you’re done, cut the power supply of the heater too.

  • For Water Heater on gas: Turn Off the Supply
  • For Electric Unit: Switch off the Breaker

Step 2. Gather the Accessories.

Measure the size of an expansion water tank by using measuring tape or thread. Remember to get some joint fixture tape. Place all the plumbing gear nearby for batter reach.

Step 3. Confirm Cold Water Supply Line.

Find the cold water supply line. Mostly it is horizontal to the water heater. You’ll need this to attach the expansion unit.

Where to Put an Expansion Tank onto a Water Heater for Best Results?

It is always recommended to install it above the water heater directly.


Place its position on the “Cold Water Supply Line” for best results.

Step 4. Install the Expansion Tank.

Install it by following these easy steps;

  1. Put the unit on a supply line
  2. Make a hole in the wall by using a drill. It is an essential step for mounting
  3. Screw-in the tank
  4. Attach the cold water supply line to it
  5. Cover the joints with plumbing tape to avoid any leakage.

How Do a Water Heater Thermal Expansion Tanks Work?

Standard water heaters use the simple rule of the steam engine. When the water heats up, it forms extra steam. The extracted moisture can cause vessels to explode due to extreme pressure. 

Expansion tanks are highly recommended if a house has a closed plumbing system. They equalize the pressure. A thermal expansion vessel creates more space for hot water to run as it is filled with cold air, preventing the system from exploding.

Does the Orientation or Mounting Position of an Expansion Tank Matter?

No, it can be installed in any direction. The mounting position doesn’t matter for a properly fixed expansion tank. You can install them upright, horizontally, and even upside down.

Step 5. Attach the Heater Tank.

Once you are done attaching the heater tank. Attach back the pipes of the water heater. Warp the spot with plumber tape. 

Secure the connection with a wrench. Don’t make it too tight.

What is the Best Pressure for Water Heater Expansion Tanks?

Between 50 PSI to 60 PSI is the advised pressure.


The air pressure can be easily checked by using a tire gauge.

Step 6. Restore the Supplies.

Switch on the water supply and let it run. Restore the power source. It is always advised to follow safety protection while handling electricity.

Step 7. Test Trial.

Have a quick test once you’re done attaching the expansion tank to the water heater. Turn on the tap and place your hand under the running water to sense the temperature of the water.

How to Know That Your Expansion Tank is Working?

The tank should sound hollow. It should be filled with air. If boiler expansion makes a dull thud, it needs repair as it may be full of water.

Quick Guideline for Sizing an Expansion Tank.

To save you from complex physics lessons or scientific formulas like ΔL = αLΔT, we have set a chart to help you buy a good size tank.

Water Heater Capacity (In Gallons)Supply PressureTank Size
50 – 6040-50 PSI2-Gallon
6060 – 80 PSI3.2 – 3.5 Gallon
8040 PSI2 Gallon
80-8550- 60 PSI3.5 Gallon
8080 PSI4.4 Gallon

Why Choosing the Right Size Expansion Tank Matter?

Water expands dramatically when it heats up. If the water pressure is too high and the attached expansion tank’s small size, there will be a blast threat due to extreme built-up pressure.


A water heater expansion vessel is very crucial. Section 608.3 of the California Plumbing Code requires a thermal expansion tank if you have a water heater. It is always advised to install it on the cold water supply line.


Comments are closed.