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recommended water pressure in system?

jack_38 Member Posts: 5
Recomended boiler pressure when boiler and cast iron radiators are on the same floor? Thanks.


  • Larry F.
    Larry F. Member Posts: 3

    What should the makeup water pressure regulator be set at on the system we are working on? (small apt complex- 2 story) do you need more info?
  • Ted_9
    Ted_9 Member Posts: 1,718

    If the boiler is in the basement, then 12psi is good.
  • JohnNY
    JohnNY Member Posts: 3,229
    It's simple math.

    One pound of pressure (1 psi) raises water 2.3 feet, or about 27 inches.
    You need to know the height of the system and then put enough pressure in the boiler to bring the water up that high.

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  • Brad White
    Brad White Member Posts: 2,398
    Enough so that

    there is about 4 PSIG residual pressure at the top of the system.

    Even though it exceeds that, 12 PSIG is a good default and is reflected in the factory charge pressure of most expansion tanks. As an absolute value, if the height difference from your lowest radiator to your highest pipe os say, 10 feet, that is 4.33 PSIG so a top pressure would be 8.33 PSIG ideally.

    Now, there are exceptions that defy the rules. Many wall-hung boilers, even if installed above the radiation on the same floor, will have minimum pressure requirements at the boiler in order to enable the burner to ignite, a basic safety function.

    All HW systems, especially those with the boiler above any radiation, should have a low water cut-off, regardless.
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