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Ken's Plumbing | Blog

Do you need a thermal expansion tank for your water heater?

Posted by Ken Flournoy on Jun 22, 2017 9:19:00 AM

thermal expansion tank.jpgAre you tired of your hot water heater always leaking? Do you need to replace yet another heater and can’t figure out what keeps going wrong?

If that’s you, you may need to install a thermal expansion tank.

To clarify, an expansion tank doesn’t increase the amount of hot water your water heater can hold. Instead, it forms a kind of pressure buffer to regulate the water pressure in your pipe system—and this can extend the life of not only your water heater, but your whole plumbing system as well.

The problem with hot water pressure

As you might recall from high school physics, most liquids expand as they heat up. As the water inside your water heater tank increases in temperature, its volume increases too, and it pushes harder against the sides of the tank.

The metals used for the water heater tank and your home’s pipes are fairly rigid by design. So unless the increasing pressure has some sort of release, it will continue to push against the pipes and sides of the tank.

In extreme cases, the building pressure can cause the pipes to burst. But the more common outcome is for the water tank to be distorted just enough to break the rubber seals over time, resulting in leaks and poor performance in general.

How a thermal expansion tank helps

A thermal expansion tank is a kind of canister that hooks on the cold water pipe feeding into the water heater. Inside the metal shell, it contains a rubber diaphragm and a pressurized pocket of air.

When the water pressure builds, water can overflow back toward the expansion tank. The flexible diaphragm allows some water to enter the volume of the tank area, taking pressure off of the rigid pipes. The air pressure ensures the water will be pushed back into the pipe system when it cools.

In this way, the expansion tank serves as a shock absorber, relieving the increasing pressure without damaging the pipes or tank.

What about older homes?

Homes built before the mid-2000s may not require a thermal expansion tank because backflow prevention devices weren’t required in residences, and the two-way flow of water allows for some natural pressure release.

However, backflow increases the risk of water contamination, so you may want to consider having a plumber come in and asses your risk, and add a backflow prevention valve and an expansion tank if necessary.


Do you need an expansion tank installed, or do you have another issue with your water heater? Give Ken’s a call at (864) 242-5511—our knowledgeable service professionals are available 7 days a week!

water heater repair

Topics: Water Heaters