How to Install a Water Heater Expansion Tank in 10 Steps (2023)

How to Install a Water Heater Expansion Tank in 10 Steps (1)

Are you worried excessive water pressure from your water heater tank will damage the unit, water supply pipe joints, and plumbing fixture valves? Did you know you can minimize these problems if you know how to install a water heater expansion tank?

Installing an expansion tank gives your primary water heater a means to minimize pressure buildup in the tank. It saves your water heater, plumbing fixtures, and other water appliances from potential damage.

Thankfully, adding a tank to your existing water heater is less complicated than you think. Let us find out.

Table of Contents

  • Things You Need for This Tutorial
    • Correct Size of Thermal Expansion Tank
    • Tools and Materials
  • Steps for Installing a Thermal Expansion Tank
    • Step 1. Turn off the water and power supply to the water heater.
    • Step 2. Prepare the water heater expansion tank.
    • Step 3. Look for the water pipe supplying cold water to the water heater.
    • Step 4. Prepare the area for mounting the expansion tank.
    • Step 5. Secure a dielectric union in the water heater’s cold water inlet port.
    • Step 6. Add a copper adapter and tee fitting.
    • Step 7. Install the water heater expansion tank pipe.
    • Step 8. Install the water heater expansion tank.
    • Step 9. Connect the pipe supplying cold water to the tee fitting.
    • Step 10. Check your work before restoring power to the water heater.
  • Conclusion

Things You Need for This Tutorial

How to Install a Water Heater Expansion Tank in 10 Steps (2)

Adding a thermal expansion tank to your water heater is less complicated than it sounds. You can complete the project in an hour or two, depending on your plumbing knowledge and availability of the following things.

Correct Size of Thermal Expansion Tank

Thermal expansion tanks are smaller than a water heater because they only serve to accommodate excess water pressure coming from the water heater.

Heating the water expands its volume by 2.5% percent for every increase of 100 degrees Fahrenheit.

It is not unusual for a 40-gallon water heater to expand by an extra 0.53 gallons upon reaching its set temperature.

That is why you need a thermal expansion tank to prevent excess water pressure from damaging the water heater and other water appliances. It often works in tandem with the temperature and pressure (T&P) relief valve.

Sizing a thermal expansion tank requires knowledge of water heater capacity.

A 2-gallon thermal expansion tank is suitable for most domestic water heaters with a 40-gallon to 60-gallon capacity and supply pressure of 40 to 50 PSI. If the water pressure is between 60 and 80 PSI, a 3.2-gallon thermal expansion tank is ideal.

(Video) ✅ Expansion Tank Installation on a Water Heater - What is an Expansion Tank? - How to Install it

An 80-gallon water heater can have a 2-gallon expansion tank if the supply pressure is 40 PSI. Increasing the PSI to 50-60 requires a 3.2-gallon expansion tank. A 4.4-gallon tank is suitable for 80-gallon water heaters with a supply pressure of 80 PSI.

Tools and Materials

Most expansion tanks have fittings and other installation hardware with the package. However, their size might be incompatible with your existing plumbing setup. It would be wise to check them and buy the necessary materials before installing the expansion tank. Click here to learn more about the right sized tankless water heater for your needs.

You will also need a dielectric union, female copper pipe adapters, short-length copper pipes, tee fitting, and Teflon tape or pipe joint compound.

A pipe wrench and pipe cutter are also essential.

Steps for Installing a Thermal Expansion Tank

How to Install a Water Heater Expansion Tank in 10 Steps (3)

Step 1. Turn off the water and power supply to the water heater.

You do not want to create a mess, electrical fires, or a gas explosion thermal expansion tank installation. That is why it would be best to turn off the main water supply line.

You might also want to close the gas supply shutoff valve if you have a gas water heater or switch off the circuit breaker supplying electricity to an electric water heater.

Step 2. Prepare the water heater expansion tank.

Unbox the expansion tank kit and lay the components on a clean surface. Most manufacturers provide a complete installation kit, including tee fittings, fasteners, and extension pipes.

However, they may not supply you with Teflon tape and pipe joint compound. It would be wise to secure these items first before proceeding.

Pro Tip: Study the expansion tank diagram to understand how to install the unit on your water heater.

Step 3. Look for the water pipe supplying cold water to the water heater.

The thermal expansion tank sits between the water heater and the cold water supply line. As such, it would be best to determine the water pipe supplying cold water to the water heater.

Look at the water heater’s top section and check if you see a water tube extending upward from it. This tubing is the cold water pipe. Follow its length until you get to the pipe’s horizontal section.

Step 4. Prepare the area for mounting the expansion tank.

Hot water heater expansion tank installation requires mounting the expansion tank above the water heater. If there is insufficient vertical space, you might want to mount it on the wall next to the water heater.

Position the mounting bracket on the wall and mark the holes for the fasteners. Remove the support and drill holes through the marked spots. Fix the mounting bracket into place, ensuring you tighten the screws or bolts.

(Video) HOW TO INSTALL A THERMAL EXPENSION TANK ON WATER HEATER

Step 5. Secure a dielectric union in the water heater’s cold water inlet port.

Remove the water pipe connected to the water heater’s cold water inlet port.

Wrap Teflon tape around the threads of a dielectric union and twist it into the inlet port. Ensure to wrap pipe-sealing tape on both ends.

Use channel-lock pliers or a pipe wrench to secure the dielectric union.

Step 6. Add a copper adapter and tee fitting.

Twist a female copper adapter onto the opposite end of the dielectric union and secure it with channel-lock pliers or a pipe wrench.

Secure a short copper water pipe to the adapter and add a tee-fitting. It would be best to ensure the tee-fitting is at least 12 inches above the water heater. This distance is sufficient for optimal vertical clearance.

You can sweat-solder the joint between the adapter and the tee-fitting for a more secure connection. Got2Learn has an exciting video on how to solder copper pipes properly.

Step 7. Install the water heater expansion tank pipe.

Insert and secure a short-length copper pipe (not more than six inches long) to the tee fitting’s side outlet to create a horizontal connection. You can use push-fit connectors or sweat-soldering for this.

Secure a female pipe adapter on the expansion tank pipe’s other end using a push-fit connector or sweat-soldering.

Step 8. Install the water heater expansion tank.

You are almost complete with the thermal expansion tank installation.

Wrap Teflon tape around the expansion tank’s threaded fitting before fastening it to the horizontal expansion tank pipe’s threaded adapter.

Most plumbers recommend tightening the connection by hand to avoid overtightening it. Too tight, and you might damage the fittings or the pipes.

Secure the expansion tank in its mounting bracket.

Step 9. Connect the pipe supplying cold water to the tee fitting.

Use the correct pipes and fitting to connect the tee fitting’s top outlet to the pipe supplying cold water to the water heater. Most plumbers use a flexible copper water line for this step.

(Video) How to Install An Expansion Tank

Step 10. Check your work before restoring power to the water heater.

Open your water supply line and check the water heater and expansion tank joints for signs of leaks. If you find any, you might want to close the water supply again and retighten the fittings.

If all goes well, finish the hot water expansion tank installation by turning on the circuit breaker or the gas supply valve.

You can also observe these steps in replacing expansion tank units.

Conclusion

Adding a water heater expansion tank can extend your water heater’s service lifespan and save you from costly repairs of damaged water appliances, plumbing, and water fixtures.

Did you find our guide on how to install a water heater expansion tank beneficial? Do you think your social contacts will find it advantageous, too? Sharing this tutorial with them is always a fantastic idea.

You can also send me your comments, feedback, or questions below, and I will be glad to answer or shed light on them.

How to Install a Water Heater Expansion Tank in 10 Steps (4)

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(Video) Installing a New Water Heater Expansion Tank

FAQs

Does it matter which way an expansion tank is installed? ›

Expansion tanks can be installed in any direction. Whether oriented uprightly, horizontally, or even upside down, the expansion tank will function properly without any adverse effects. When putting an expansion in an abnormal position (specifically sideways or horizontally), make sure to support the tank.

How close should an expansion tank be to a water heater? ›

The items which should be installed in sequence in the cold water line are (1) the EXPANSION TANK must be installed at least 18 inches away from the cold water inlet fitting on the water heater, (2) the PRESSURE GAUGE, and (3) the PRESSURE REDUCING VALVE, if required, see Figure 1. 3.

How much does it cost to install an expansion tank? ›

The job of the thermal expansion tank is to absorb the extra water volume so that the excess pressure does not cause undue wear and tear on the water heater and other fixtures in the home. The cost to install a new Thermal expansion tank can range from $279 to $443.

How much air pressure should be in an expansion tank? ›

Expansion tanks are pre-charged with a 40 PSI air charge. If the inlet water pressure is higher than 40 PSI,the expansion tank's air pressure must be adjusted to match that pressure but must not be higher than 80 PSI. *Highest recorded inlet water pressure in a 24-hour period of regulated water pressure.

Do I need to install an expansion tank on my water heater? ›

If your home has a “closed” plumbing system, then yes, you'll need an expansion tank. You see, homes have either an open or a closed plumbing system. A closed plumbing system prevents water from flowing in the reverse direction (i.e., water won't flow back into city lines once it enters your home's pipes).

What line does the expansion tank go on? ›

Although expansion tanks can be installed on the hot side, we strongly recommend they be installed on the cold line, downstream of the shutoff valve.

Can you install water heater expansion tank sideways? ›

Can a water heater thermal expansion tank be installed sideways/horizontally? Most expansion tanks are designed to be installed vertically (stem up or stem down). You can install one sideways, but it will shorten the lifespan unless it is designed and specified by the manufacturer for horizontal installation.

What size expansion tank do I need for a 40 gallon water heater? ›

General Guidelines for Sizing an Expansion Tank
Water Heater CapacitySupply Pressure (psi)Expansion Tank Size
40 to 60-gallon40-50 psi2-gallon
40 to 60-gallon60-80 psi3.2-gallon
80-gallon40 psi2-gallon
80-gallon50-60 psi3.2-gallon
1 more row

Which way up should an expansion vessel be fitted? ›

The expansion vessel should be installed vertically above the pipe with the water connection at the bottom and the air valve upper most.

What pressure should my expansion vessel be? ›

Summary. Expansion vessels, also known as expansion tanks, keep the pressure in a combi boiler stable while water heats and cools. They are typically located inside the boiler casing. The typical pressure a boiler system should be set to is 1 bar.

Does an expansion tank need to be supported? ›

Typically, the tank is only required to be supported when installed in the horizontal position. Most smaller tanks are designed to be supported by the plumbing, when installed in the vertical orientation. The most common recommendation seems to be, to install the tank vertically below the plumbing.

How long does it take to install an expansion tank? ›

Your new tank should be installed by a licensed plumbing professional within 2 hours.

What size expansion tank is required for a 50-gallon water heater? ›

For a 50-gallon water heater, you require a 2-gallon expansion tank. Depending on how high your water pressure is, however, you may need to go up a size to a 4.5-gallon expansion tank. The only two factors to consider when picking your expansion tank are water heater size and how high your water pressure is.

How long does a expansion tank last? ›

Depending on the quality of water a Thermal Expansion tank lasts an average of 5-8 years. Finally, testing your Thermal Expansion Tank is important and should be tested once a year when you flush your water heater.

How do you bleed air from an expansion tank? ›

3 Answers
  1. Turn off the valve that auto-fills the system from your cold water line.
  2. If you have one, open a valve or bleeder on the top of your expansion tank. ...
  3. Open a drain valve and drain a suitable amount of water.
  4. Close drain valve and re-open valve you closed in step 1.

How do I check the pressure on my water heater expansion tank? ›

To check your expansion tank pressure, you should use a standard tire gauge and press it against the valve on the top of the tank. You can then adjust the pressure with a hand pump and raise the pressure as needed. If pressure is too high, simply press against the Schraeder valve to release air inside the tank.

What causes expansion tank to fill with water? ›

As hot water enters the heating system, the pressure in the system increases. As pressure increases, the diaphragm in the expansion tank is pushed down. This compresses the air in the tank, creating more space for excess water to enter.

How do I add pressure to my expansion tank? ›

Adjusting the Pre-Charge of a Thermal Expansion Tank - YouTube

Will an expansion tank increase water pressure? ›

The expansion tank contains air, which is highly compressible. Expanding water from the water heater can flow into the expansion tank, where the air compresses, making room for the increased volume of water. Water pressure in the system doesn't increase significantly.

Can PEX be used for expansion tank? ›

Cut a piece of PEX to run between the expansion tank and the tee-fitting that you inserted in the hot water tank cold water supply line. If you have other fittings between the two, you will need to cut pieces of PEX to connect those as well.

What happens if expansion tank fails? ›

Oftenthe diaphragm dividing the two systems will fail, causing the two systems to become one. When this happens, the expansion tank turns into a “dead leg” that will eventually cause damage and premature failure to your water heater.

How do you size an expansion tank? ›

How to size and select a proper expansion tank - YouTube

Where should an expansion tank be placed? ›

The tank can be installed anywhere in the cold-water line between the house's main valve and water heater, or on the hot-water line within 3 ft. to 5 ft. of the water heater. An expansion tank should be installed in conjunction with a pressure-reducing valve in high-pressure situations.

How do I check the water pressure in my house? ›

The most accurate method is to buy a pressure gauge from your local hardware store and hook it up to a hose faucet. Check the pressure when all other faucets and water-using appliances are turned off to get a baseline reading. In general, you want the household plumbing to provide between 30 and 80 psi.

What causes too much pressure in hot water heater? ›

Why is My Water Heater Building Up Too Much Pressure? If your water heater is building up too much pressure there's likely three reasons. Either the temperature is set too high, there's a malfunction, or the water heater doesn't have an expansion tank.

What happens if expansion tank pressure is too low? ›

Pre-charge pressure that's too low may be indicated when the tank is full of water. Low pressure can cause too much water from entering the tank. It could also indicate that the diaphragm is no longer functional, which means that there is nothing to prevent the water from entering.

What is the difference between an expansion tank and a pressure tank? ›

The biggest difference between pressure tanks and expansion tanks is in where they're used. Expansion tanks are installed above a water heater and help to protect it when hot water expands. Pressure tanks are installed near your well pump and help to protect and extend its lifespan.

Does expansion vessel go on flow or return? ›

An Expansion Vessel is open to water one end and connected to our system normally on the return side. It has a compartment filled with air separated from the system by a flexible membrane (air unlike a fluid will compress). As the water heats up it will enter the vessel and begin to compress the air.

How do I know if expansion vessel failed? ›

If you think the vessel has failed, unscrew the plastic cap from the pressurisation valve (it's like a car tyre valve). Momentarily depress the pin in the valve to release a little pressure. If water comes out of the valve you have a definite expansion vessel fault.

What happens if expansion vessel pressure is too high? ›

Too little air in your expansion vessel and the pressure may become too high. resulting in the water coming out of your pressure relief valve. Too much air could result in an over pressurised system, this could also result in water coming out from the pressure relief valve.

What happens if expansion vessel is too small? ›

When water is heated, it can expand to between four and nine per cent of its original volume. This means that an expansion vessel that is too small may not be able to perform its job sufficiently and won't take enough water out of the system to bring the pressure back down.

How long does it take to install a 40 gallon hot water heater? ›

WATER HEATER INSTALLATION PROCESS

If there are no issues or complications, a licensed plumber should be able to complete the process in 2-3 hours.

Where should a water heater expansion tank be installed? ›

There is a need to fix an expansion tank near a water heater. You can place it at any spot on the water supply line. Most times, it stays fixed with a T at the cold water inlet that supplies the water heater. However, you can install it on the part of the cold water supply line.

Does expansion tank go on hot or cold side? ›

Although expansion tanks can be installed on the hot side, we strongly recommend they be installed on the cold line, downstream of the shutoff valve.

What size expansion tank do I need for a 40 gallon water heater? ›

General Guidelines for Sizing an Expansion Tank
Water Heater CapacitySupply Pressure (psi)Expansion Tank Size
40 to 60-gallon40-50 psi2-gallon
40 to 60-gallon60-80 psi3.2-gallon
80-gallon40 psi2-gallon
80-gallon50-60 psi3.2-gallon
1 more row

What size expansion tank do I need for a 50 gallon water heater? ›

For a 50-gallon water heater, you require a 2-gallon expansion tank. Depending on how high your water pressure is, however, you may need to go up a size to a 4.5-gallon expansion tank.

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