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Water pressure for a converted steam radiator system?

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Chuck_17
Chuck_17 Member Posts: 145
Sorry if this question has been answered many times - it is hard to search:
A old steam system with cast iron radiators has been converted to hot water.
What is a safe maximum water pressure for the system?

System in question was converted years ago.
For a renovation I'll use the pressure to size the expansion tank.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    Use the lowest possible pressure you can to ensure just filling the highest radiators. Multiply the elevation from the point at which you are measuring static pressure to the highest radiator, in feet, by 0.45, and add no more than 2 psi, to get the cold pressure. If possible, oversize the expansion tank to minimize pressure changes when the system heats.

    The pressure tank must be near the inlet to the circulator(s) ("PONPC"). Anything else is not an option.

    And good luck. It may well leak anyway...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Chuck_17
    Chuck_17 Member Posts: 145
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    I'll check the existing boiler relief valve pressure and use the same on the new boiler.
  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    The boiler pressure relief valve rating is determined by the boiler rating -- both the maximum working pressure and the burner input. You must use the correct relief valve for the specific boiler.

    The pressure relief valve pressure rating has nothing to do with the correct system working pressure, which is controlled by the automatic boiler feed valve (if any) and the expansion tank preset pressure.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England