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Thread: What pressure should a thermal expansion tank be at?

  1. #1
    DIY Senior Member vtxdude's Avatar
    Join Date
    Nov 2009

    Default What pressure should a thermal expansion tank be at?

    When the plumber put in the the BW water heater he set it at 60 psi...said it was at 30 psi....

    Is there a set standard at what it should be set at? Id PSI is too high what does that affect?


    PS the expansion tank is mounted upside down if that matters.

    See here for pics

    Last edited by vtxdude; 01-11-2010 at 10:50 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    The static pressure for the expansion tank should be about the same as you 'normal' pressure reading. So, if the incoming water pressure is around 60#, it's fine. If you take a reading after it is in the system, it will be whatever the water pressure is...to test and change, you need to relieve the water pressure on the bladder first, then adjust. If it's balanced with the static water pressure, there's very little movement of the bladder. Otherwise, it is potentially stretched further than needed, and it might wear out faster. Orientation doesn't matter except when it fails, with it sticking up, you'll drain all of the water forced into it all over. Doesn't happen often, but keep that in mind. The tank should be supported so if it does fail and fill with water, the stress to the piping and fittings isn't great.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default psi

    As a practical matter, ANY pressure above zero and below 150 will accomplish the purpose to some extent. The closer it is to the normal pressure in the system the better it works. If the initial pressure is less than the normal pressure, it WILL stabilize at the house pressure as soon as you turn the water valve on.


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