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Thermal Expansion FAQ

Expansion Tank Frequently Asked Questions

  • What is a thermal expansion tank?An expansion tank is a small tank that is attached to the inlet cold-water supply pipe of a water heater. 
  • Why do I need an expansion tank?Water expands when heated, creating increased pressure in a water heater. In the absence of an expansion tank, the water will look for a way to escape. In older systems, the hot water will backflow through the cold-water pipe through which it came and end up back into the public water supply.  Backflow can lead to contamination of clean water. The national plumbing codes mandate a backflow preventer. Because of the backflow preventer, the water has nowhere to go except the pressure relief valve located on your water heater.  If your relief valve is working properly, it will spill water onto the floor. The expansion tank provides a pressurized air cushion that absorbs expanded water, keeping pressure in the system within safe levels. If left unchecked, the constant fluctuations in water pressure will damage the heater and associated piping.
  • How soon will Granger-Hunter Improvement District install a backflow device at my meter?In the future, GHID plans to install a backflow device at every connection.  With over 27,500 connections, this will take some time.  Before a backflow device is installed at the meter, GHID will deliver a letter giving 30 days’ notice.  However, if there is an emergency repair from a leak on the system, GHID will not be able to give advanced notice.  In this case, a notice will be given immediately following the repair
  • Where can an expansion tank be purchased?Expansion tanks can be found on-line or at any home-improvement or plumbing supply store if you are installing it yourself.  Tanks range from $40-70.  If you choose to have a certified plumber install an expansion tank, it may range from $200 - $400.  We recommend getting multiple quotes before hiring a plumber.
  • Do water heater manufacturers specify a need for an expansion tank?Yes, all water heater manufacturers state a similar requirement to maintain warranty coverage if the system contains a one-way device like a backflow preventor.
  • Is it necessary to install an expansion tank on a tankless water heater?Plumbing code does not require an expansion tank with a tankless water heater unless a storage tank is added to the tankless heater in a closed system. 
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