Our thermal expansion tank is installed after the meter and feeds into the house and hot water heater. It seems like it should have been installed immediately prior to the water heater...

Can I install a water softener after the thermal expansion tank or should I try to install it between the meter and thermal expansion tank?

  • You can put the expansion tank about any place there should be a check valve to stop back flow to the meter it really doesn’t matter where it is.
    – Ed Beal
    Sep 22, 2020 at 1:02
  • @Ecnerwal I think it’s related but I wouldn’t say it addresses it completely. I do think the accepted answer adds value to the DIY community. Sep 23, 2020 at 1:22

1 Answer 1


I don't think this should be a problem, water softeners I have seen do not have check valves in them so water can flow through both ways. It's only after a check valve where expansion capacity is needed.

Many homes do not even have an expansion tank, they are most frequently found (at least in my area) where there is a pressure regulator (which contain a check valve) installed after the meter. In that case you need an expansion tank (especially with a water heater) because of the additional pressure warmer water will create in the system which needs to be relieved. If there are no check valves in the system the entire city main can serve as the expansion tank (water flows backwards through your meter).

  • And you get charged both directions on the meters I have seen they only detect flow not direction.
    – Ed Beal
    Sep 22, 2020 at 1:05
  • @EdBeal in many places there is a check valve at the meter. At the previous house I lived in, the water company didn't meter the water usage at first. Years later and due to gov't regulation they installed water meters and check valves. The house didn't have an expansion tank. Then the pressure relief valve on the water heater would occasionally let out some water. Put a pressure gauge on it and it was over 100 psi. Added an expansion tank and problem solved. Sep 22, 2020 at 13:52
  • I have seen more without check valves including the tracks we built back in the 70’s. I mentioned this because without a check valve the meter can run backwards, with a check valve the closed loop pressure can do damage when the water heater cycles and heats the water. That’s why I mention them.
    – Ed Beal
    Sep 22, 2020 at 15:52

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