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Balancing Steam systems...main vent timing/sizing

DomesticEngineer Member Posts: 18
edited December 2020 in Strictly Steam
So I'm going to pull off main vents and time them to see how long it takes for them to get hot in order to help me size replacement vents. Question is this: Do I need to close off all my radiators first or does venting that occurs there affect this minimally? I also assume each vent should be done separately? I have two that are right next to each other in the basement (and a 3rd on the 2nd floor).



  • JohnNY
    JohnNY Member Posts: 3,230
    What registers, Domestic Engineer? Is this a steam system or forced air?
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • DomesticEngineer
    DomesticEngineer Member Posts: 18
    I have 7 radiators in the house (6 main floor, one upstairs). Steam system.

    I put this on hold over the summer, then I was swamped with 3 classes on top of working full time so details about my system are a little rusty. I think I have a 2 pipe with cold returns.

    After measuring mains for venting I'll then focus on replacing radiator vents.

    I have just enough knowledge in physics to know that sometimes I apply things well, and sometimes I complicate things too much. Consulting probably isn't necessary because, per previous posts, replacing vents probably won't make system run all that much better due to improper header and wet steam, etc.
  • Jamie Hall
    Jamie Hall Member Posts: 23,313
    I you have two pipe with returns and radiator vents, either your system is very old indeed -- 1890s -- or something is very wrong.

    That said, adding to your main venting shouldn't disturb the balance of the radiators (if they are one pipe), unless the existing main venting is woefully undersized.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ethicalpaul
    ethicalpaul Member Posts: 5,702
    This test gets weird with multiple mains. If you test them individually you’ll end up with more venting than you need. But that’s probably the way to go.

    don’t worry about the radiators. The vast majority of steam will prefer to go to the open main vent port

    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el