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Two-pipe system with only one vent?

I have a two-pipe steam system, over 2 million btu, and I can only find one vent (Hoffman 75), which is at the end of a horizontal supply run (at a steam trap) near the basement ceiling. No radiators have vents; just the open/close valves with knobs.

The system works. The building is 80 years old; I've had it for 5 years without major heating issues, except that some apartments' radiators get hot faster than others.

Does a two-pipe system only need one vent?


  • Steamhead
    Steamhead Member Posts: 16,728
    The radiators

    are vented thru the dry (overhead) returns, to a device near the boiler that probably doesn't look like a vent. Often the steam mains vent thru radiator-type traps to the dry return as well.

    Take some pics of the piping near the boiler and we can probably point it out.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • cmahrle
    cmahrle Member Posts: 15
    I think I see

    what you are referring to, thank you.

    What might be the reason they would have put that small air vent on at all, then? (It's just past one of the steam traps.)
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