Water Heater Expansion Tank - Do you need one?


water heater expansion tank

A 30 to 40 amp water heater needs a 8-gauge wire, a 25-amp water heater needs a 10-gauge wire, and a 20-amp water heater needs a 12-gauge wire. It is best to use a wire that is larger than needed when you are going to wire a water heater. Water heaters come in different sizes and need different wire sizes for each.

What is an expansion tank?

expansion tanks

An expansion tank is a device/tank that is added to an existing hot water heater to relieve pressure that is built up in the system overtime. Without an expansion tank, you might experience inconsistences in the flow of water through taps or faucets.

Do you need a water heater expansion tank?

The answer is yes. An expansion tank is a vital component that helps to regulate the pressure in your plumbing system and prevent damage to your water heater and pipes. As water is heated, it expands, which can put a lot of pressure on the pipes and other components. Without an expansion tank, this pressure can cause leaks, damage to fittings, and even burst pipes. An expansion tank helps to absorb this excess pressure, maintaining the balance of pressure in the system and protecting your water heater and plumbing from damage. In addition, it helps to prevent the water heater from becoming overworked, prolonging its lifespan and efficiency. Therefore, it is important to have a properly sized and maintained expansion tank to keep your water heater and plumbing system functioning at their best

What is A Thermal Expansion Tank?

A thermal expansion tank is the same as a water heater expansion tank as it relieves the water pressure in a water heater tank to avoid damages to the system.

What is Thermal Expansion?

Thermal expansion is the term used to describe the way water expands when it is heated. When you heat water in a closed system, it will expand by a small percentage. This small percentage is however a problem in systems that hold lots of water. A system that holds

What is a water heater?

water heater

A water heater is a device used to heat the water in homes and other buildings. They come in different types that use different sources of energy to operate. Some use solar power, electricity, and some use propane fuel.

How to test if your thermal expansion tank is working?

Before performing any checks on your expansion tank, ensure that there are no damages or leaks on your tank. If you see any of these signs, use the water shutoff valve to cut-off any water to the system. The next step would be to contact a license professional to come in and fix the system. However, if there are no sign of damage or leaks, follow the steps below to check if your expansion tank system is working properly.

  • Check Pressure
  • The most fool proof way to check if your expansion tank is working is to do a pressure test. below are the steps to take to perfect this test.

    1. Turn on a tap on the outside of your house for about 20 seconds. This will allow any pressure in the system to be bled. The bled pressure will be from thermal expansion in your tank and will leave pressure that is set to your PRV (pressure relief valve).
    2. Connect your water pressure gauge to the tap you turned on earlier to find out what the pressure is in your system.
    3. Use the main shut off valve to shut off all water leading to your house.
    4. Next open another faucet or tap to relieve any other pressure that might be in your system.
    5. Connect the pump to to your expansion tank via the Schrader valve.
    6. You will know how much pressure (air) is in your tank by looking on the pump's gauge. The pressure in your tank at this point should be the same as the pressure you read earlier in step #2.
    7. Adjust your pump to match the pressure of your tank's pre-charge.
    8. After both the pressure in your water heater and expansion tank are the same, you can disconnect your pump and restore water to your home.
  • External Tapping
  • One way to check if your expansion tank is working is to tap on the side with some sort of metallic object. This is one of the easiest test to perform on your water heater expansion tank. An expansion tank should have pressurized air at the top half and have water from your home's plumbing system at te bottom half. When you tap on the side of the tank with a metallic object, you should hear two different and distinctive sounds when you tap on both the top and bottom half.

How long does an hot water expansion tank last?

Hot water expansion tanks usually last anywhere from 5 to 10 years. Matching the home's water pressure to the air pressure in your expansion tank can prolong the life of your expansion tank.Irregular surges in the air pressure will damage your expansion tank.

Can Your expansion tank leak?

Yes, your expansion tank can leak. This can happen when there is a lot of wear and tear on the system. The tank can also leak if it was not install correctly.

Which size expansion tank should you get?

The proper size expansion tank to get for your system will all depend on the type of system you have and the volume of water you have.

Water Heater Tank Capacity Pressure (Supply PSI) Recommended size of expansion tank
80 Gallons 80 Psi 4.4 Gallons
80 Gallons 50-60 Psi 3.2 Gallons
80 Gallons 40 Psi 2 Gallons
40 - 60 Gallons 60-80 Psi 3.2 Gallons
40 - 60 Gallons 40 - 50 Psi 2 Gallons

How to install a hot water expansion tank?

Installing an expansion tank is not a hard diy job if you know your way around the water system in your home.

Tools needed for the job

  • Thermal expansion tank
  • Pipe wrench or channel-lock pliers
  • Threaded copper adapter
  • Dielectric water heater nipple
  • Pipe-sealing tape
  • 3/4-inch copper female-threaded unions (2)
  • 3/4-inch copper pipe
  • Extra 3/4-inch copper fittings
  • 3/4-inch copper tee-fitting
  • Equipment for soldering
  • Copper flex pipes

Some items might not be used while you do the job but it is always best to have everything at hand that you might need.

Steps to take
  1. Firstly, attach the dielectric union to your cold water entry port. To get a perfect seal, you should wrap the threads of the dielectric union with pipe sealing tape.
  2. Use pipe sealing tape to ensure that there is a strong seal. After adding pipe sealing tape around the top of the union, thread a a copper adapter to the said union point.
  3. Attach a tee fitting water heater's dielectric union side adapter.
  4. The next step to attach the expansion tank pipe. Try not to make this attached pipe any more than 6 inches. The extension tank pipe should be added to the outlet side of the tee-fitting.
  5. You will always get a great seal when you use pipe-sealing tape. Add pipe-sealing tape to the threading of the expansion tank and next add it to the horizontal pipe's adapter.
  6. The final step is to connect the top outlet of the tee fitting to the pipe that supplies your cold water.

What happens if you use the wrong size hot water expansion tank?

Using a hot water expansion tank that is larger than needed for the current system you have is not a bad thing. If you do buy an expansion tank that is larger than you need, the on;ly downside to it would be you spending too much money than you need. on the other hand, if you buy an expansion tank that is too small for your current water heater, you will run the risk of damaging both the water heater tank and the expansion tank.


A water heater expansion tank is necessary as it helps to keep your expansion tank running in top performance. You do not have to purchase the most expensive one. Just one that is meant for the size water heater tank you have.

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About Author:

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Hi, I'm Kevin Pommells, a lover of camping and the great outdoors as everyone says nowadays. I'm also a passionate soccer fan and the proud owner of CamperRules.com, a website dedicated to helping campers and outdoor enthusiasts make the most of their adventures. With years of experience exploring the wilderness and a deep love for the sport of soccer, I'm always looking for new ways to combine my two passions and share my knowledge with others. Follow me for tips, tricks, and insights on all things camping and outdoor recreation.

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