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How to size an expansion tank?

Please let me know in great detail, all relevant areas that I would need. Thank you very much.


  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Start with

    1) Volume of the system in gallons

    2) Expected maximum operating pressure in PSI Absolute. (Add 14.7 to gauge pressure to get absolute pressure if at sea level.)

    3) Initial cold fill pressure (static pressure) at point of tank connection, more specifically the elevation at which the tank will reside; this too is expressed in PSI Absolute.

    4) Maximum design temperature.

    There is software available for selecting tanks, whether conventional or bladder/diaphragm type.

    You will note that if the tank is higher in the system (say an attic or upper floor) the tank will be smaller. Likewise a cooler maximum operating temperature will get you a smaller tank than one that runs hotter.

    Hope this helps.

  • Matt_49
    Matt_49 Member Posts: 4
    Expansion Tank Spreadsheet

    Here's a spreadsheet that is taken right from the Amtrol sizing guidlines.

    Be sure to use the coldest and hottest water temperatures the system will experience (you likely filled the system with 45 or 50 deg water).
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