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Understanding ounces of CFM in a one pipe steam system

I'm using the great document - Balancing Steam Systems Usings a Venting Capacity Chart

To select radiator air vents based on venting capacity the charts have 3 columns - 1oz, 2oz, or 3oz, CFM. How do I understand the CFM of my system?

I'm a homeowner with a one-pipe steam system the pressuretrol is set to cut in at 1 PSI and out at 2 PSI. The mains are 2 inch pipes.


  • ChrisJ
    ChrisJ Member Posts: 15,788
    Use the 1oz spec.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Jamie Hall
    Jamie Hall Member Posts: 23,450
    The CFM is "cubic feet per minute" and is related to the pressure across the vent, which is measured in ounces (per square inch).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gsmith
    Gsmith Member Posts: 433
    Both above are correct, but to elaborate a bit more, the CFM is the cubic feet per minute of air which the radiator vent will release at 1 oz/square inch pressure ( or 2 or 3 oz/si if you run at those higher pressures and use the other two charts). I guess in theory the total of all the vent rates (adding all the vent figures together) should approximately equal the steam production of your boiler in CFM at each pressure.
    EBEBRATT-Ed Member Posts: 15,631
    As @Garry Smith pointed out the oz of steam pressure is the pressure your boiler runs at.....thats the steam line pressure.

    CFM is the amount of air contained inside the pipes that the vens have to vent