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Expansion tank pressure

Im embarrassed to ask having been in the business for years but I need some education. When putting a new boiler into operation, what is the proper procedure for ensuring that the expansion tank pressure is correct? what is the relationship between the expansion tank pressure and setting the pressure reducing valve? Once again I have a new installation and no circulation on the third floor. Help me comrades


  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Exp tank pressure

    The expansion tank should be charged to 12-14PSI at 0 boiler pressure. This presumes a 3 story house. You may need 16psi to reach the 3rd story, use the fast fill on the PRV to increase the pressure on purging.
  • MikeyB
    MikeyB Member Posts: 696
    Tank sizing

    You can also type in Expansion Tank Sizing in the Site Search bar in the top right corner and search through some good info, also check out Amtrol's website
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited September 2009
    Generally speaking...

    you NEED 1/2 PSI per vertical foot of system elevation, PLUS 5 PSI to avoid air trapping at the top of the system. So, if you have 10' per story, then you are looking at roughly 25' of elevation from the top of the boiler to the top of the system (assuming radiant floor or baseboard, and boiler located in basement. If using FCU's in the attic, then add that elevation.) So, 1/2 PSI per foot = 12 PSI, PLUS 5 PSI = 17 PSI fill pressure. I usually recommend that the bladder of the tank be pressurized to the same pressure as the system fill pressure. This keeps the acceptance volume of the tank intact, otherwise you lose a portion of the acceptance factor due to the tank diaphragm being partially distended before the fluid actually starts expanding.HTHME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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