What is an Expansion Tank

In Plumbing by Mark Goodman

The expansion tank located adjacent to or near the water heater heater is to protect the water heater and the pressure relief valve from water pressure emanating from surges in the water source.

expansion tank 1
water heater w/ expansion tank

Is an Expansion Tank Required

This depends. Some cities, counties or municipalities do require the use of an expansion tank, even if your house is serviced by a private well system, rather than public water. If you aren’t sure, you may want to check with your local governing agency. However, even if the use of an expansion tank is not required by your local codes, most water heater manufacturers do require the use of a properly installed expansion tank to validate their warranty. Be sure to read your warranty information closely. Also, this is a relatively new component, so older water heaters typically won’t have an expansion tank, nor are they typically required on older water heaters by the local municipality or manufacturer.

How to Maintain Your Expansion Tank

If you’re installing a new water heater and expansion tank (or having it installed by a professional contractor), make sure the expansion tank is installed according to the manufacturer recommendations and specifications. If you are moving into a new home that already has an water heater with an expansion tan, there are a couple of things to look for.

  • Make sure the expansion tank is properly supported with an appropriate support strap. The expansion tank should be installed on the cold water line.
  • Check the connection of the expansion tank to the water line. Water lines in existing homes are typically copper and the connection for the expansion tank is typically steel. These are dissimilar metals that will eventually result in corrosion and leaks without the benefit of a dielectric union or brass fitting. This can be checked with a magnet.
  • Expansion tanks can sometimes become water logged. A quick way to check this is to knock on the expansion tank. A hollow, empty sound is good. If you hear a dull thud, it’s water logged.