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Main Vent Location

Iam adding a 2nd Main to a 1 pipe steam system. I have piped the 2" line off the header, and my old IBR GUIDE shows main vent should be "not less than 15 inches" before reducing elbow and return. My question is this still the practice today, since my other existing main vent is just 6 inches from return. Everyone I speak to tells me to keep this return around 6 inches? My question is what is the correct distance for the main vent before the return? Thank you to all the Steam Gurus.


  • Well......

    Since you asked, right after the last take-off to the radiators.

    The steam is everywhere important by then, and it can push against the air beyond it with no bad effects. It'll shut off on pressure quicker, it'll force steam out of the main quicker, and it is cheaper to make compressed air than compressed steam.

    If you have a lot of piping beyond the last take-off that stays high, you can put it waaayyy back from the end.

    Too close to the end would be the problem.

    A wise steam man from Baltimore showed me that.

  • ed broderick
    ed broderick Member Posts: 15
    Main Vent

    Thanks Noel for your reply and good advice. I will use a short nipple before I pipe the return. By the way, should the nipple for the main vent be in the 6 to 8 inch range over the main? Thank you again. Ed
  • yes

  • Steamhead
    Steamhead Member Posts: 16,725
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    And the rest of us are just a bunch of Wise guys!

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