Water Heaters and Expansion Tanks

The need for an expansion tank with new or existing water heaters has been a point of confusion for many.  The information below will hopefully provide clarity on this issue for plumbers and homeowners alike.

Where Required

Expansion tanks are required when a plumbing system contains a check valve, backflow preventer, pressure reducing valve or a pressure increasing pump. Most homes in Fairfax County, the town of Vienna and the city of Falls Church do not require any of these devices, and therefore, an expansion tank is not required.

Some neighboring jurisdications uniformly require a backflow preventer, and as a result, all homes there will require the expansion tank.  However, this is NOT the case in Fairfax County.

How to Eliminate

If you own one of the few homes in Faifax County with an expansion tank, you may be able to eliminate it with the inclusion of one of the valves listed below.

  • Pressure reducing valves with an integrated, multi-direction bypass (identified with a "B" in the model number) when the street pressure is over 80 PSI.
  • Fill valve and thermal expansion relief valve.
  • Combination ball valve and relief valve.
  • Ball valve with integral thermal expansion relief valve.
  • Shutoff/thermal expansion control valve.

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Technical Questions: Web Administrator

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