What is a Thermal Expansion Tank?

Home » What is a Thermal Expansion Tank?

What is that small tank above my water heater?  I hear that question a lot.  The answer is it’s a thermal expansion tank.  But what is that?  Simply put, when your water heater is on, as it heats the water, it expands (i.e. thermal expansion).  The tank gives that added pressure a place to go instead of building up in your plumbing system.

Is a thermal expansion tank important?

Yes, not to mention it’s required by code in most municipalities.  The tanks become necessary when water districts started putting check valves on their meters.  Also, back-flow preventers or pressure reducing valves installed on an incoming water supply causes the system to become closed.  When thermal expansion occurs, the pressure can build to well over 100psi causing potential damage to your plumbing system.

Water heaters are more expensive than ever and are only going to get more expensive.  Anything you can do to lengthen their life is a good idea.

Once installed, thermal expansion tanks should be checked occasionally to make sure the device is not leaking and is still performing properly.  If the temperature and pressure valve is popping off on your water heater, it’s a good indicator the expansion tank has failed.  If you don’t have one or aren’t sure yours is working, give us a call as they should be installed by a professional.

The link below provides a nice explanation of thermal expansion tank with some nice illustrations as well.

Bradford White Expansion Tank Brochure

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If you are in Columbia, MO or the mid-Missouri area and believe you have a plumbing problem, contact us.