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No vents on steam mains?

I have a one pipe steam system, with 8 radiators on two floors--not very big. Built in 1950.

Question: I don't see any vents in the basement on the mains. Is that possible that there is only the radiator vents?

Question 2: The mains exit the boiler in three directions. Two of the mains then reconnect on the other end of the basement, forming a big loop. Why?


  • SteamheadSteamhead Posts: 13,563Member
    That system should have main vents. A lot of coal-fired systems originally didn't, but oil- or gas-fired ones definitely need them.

    The "big loop" might work, but it's better for each half of the loop to have its own return connection and main vent. This way steam in one main can't affect the other main. Does the return connection drop to near floor level?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • heatinghorseheatinghorse Posts: 13Member
    Thanks, to your question, no, the loop does not drop near the floor--it runs along the basement ceiling back to the boiler.

    Do you think the loop is intended to have a separate return for the condensate?
  • SteamheadSteamhead Posts: 13,563Member
    Someone cheaped out. Each section of the main should have its own return. If that means running another return line overhead, so be it.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • heatinghorseheatinghorse Posts: 13Member
    Sorry, each main needs a return, in a 1-pipe system? I though the return runs through the same pipe?
  • Danny ScullyDanny Scully Posts: 1,220Member
    Are you sure it’s not just a circuit?
  • the_donutthe_donut Posts: 374Member
    Pictures >= thousand words. You could have a counterflow system. This system may not have a main vent. If every run to the radiator is equal, in theory no main vents are needed as steam will arrive to every radiator at same time, but you are paying for steam pressure to force air through a tiny radiator vent.

    Pictures of mains, near boiler piping and return lines will be helpful. Also approximate lengths and diameter of pipe would be helpful in sizing vents.
  • heatinghorseheatinghorse Posts: 13Member
    I'll post some pics later.

    I am having a problem with two of the upstairs radiators not getting steam as fast as the rest of the house. The near-boiler piping is not insulated, which could be why, but alternatively maybe it just needs some vents.
  • Jamie HallJamie Hall Posts: 12,099Member
    Before you start cutting in main vents -- though they'd help for sure -- try putting slower vents on the radiators which are heating faster.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JimmyNJJimmyNJ Posts: 93Member
    Definitely possible that you do not have any Main vents as I made the same discovery a few years back. The original system was coal fired so it didn't need it so I ended up installing 3 Gordon #2's and it really did help get steam into the rads faster but to Jamie's point above, better to try to balance the rads first.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,497Member

    Until you post some pictures everything is a guess.
  • Mike_SheppardMike_Sheppard Posts: 643Member
    @heatinghorse I believe Steamhead is referring to a parallel flow steam system, as opposed to a counterflow steam system.

    Parallel steam system will have returns from the ends of the mains. Steam will feed up into the radiators and condensate back down the same pipe. Condensate will drain to the end of the main and return to the boiler through a wet or dry return.

    In a counter flow system the condensate from the radiators flows back to the boiler through the main, rather than a return.

    It all depends on what you have. Pictures!

    Old coal systems sometimes connected the ends of the mains together to form one large loop. A coal fire burned for much longer than a gas or oil burner, so there was no rush to get the air out fast, which is why there are no main vents. Now that it’s gas/oil, it will cycle on and off and and getting air out fast enough is an issue.

    What I believe Steamhead is saying, is it would be best to separate those connected mains, and add another return for the third main (if it’s a parallel flow system) so that you can add air vents at the end of each main.
    Never stop learning.
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