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steam in dry returns

i was checking out the venting of my main lines today and noticed that the dry returns started to heat up after the steam hit the vents at the ends of the mains..
that didn't seem right to me.. why would i be getting steam in there ? and is it a problem i need to try and correct ?


  • Jamie Hall
    Jamie Hall Member Posts: 22,918
    Depends on how your system is piped. The term "dry return" is a little flexible -- in most two pipe systems, which have crossover traps or the dry return isn't physically connected to the steam main, the dry return really is just that, and shouldn't have steam. In many systems, though the "dry return" is just a continuation of the steam main -- this is particularly true of one pipe systems. In the latter, the dry return, even if not vented, will gradually get steam in it.

    The former system, or any two pipe system which has true dry returns (not connected to the steam main at the end) then no, steam shouldn't get in there.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Is this 1-pipe or 2-pipe? Are the vents at the end of the supplies, or at the end of the dry returns, (ideal location)?
    What is the verified backpressure of venting when air is being expelled from the pipes, (less than 2 ounces is ideal)? If the pressure is too high, the remaining air in the top of the wet returns can be compressed, and the steam edge moves further downstream.
    As the steam condenses, the hot condensate will flow into the wet returns, and it is fairly warm, but not steam hot.—NBC
  • JohnNY
    JohnNY Member Posts: 3,226
    What makes you think you're feeling steam and not condensate?
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • coelcanth
    coelcanth Member Posts: 89
    this is a one-pipe system with divided mains,
    one each for the front and back of the house and one for each floor. there's two floors, so four mains i guess..

    each main is vented at a tee at the end furthest from the boiler, after the last riser. one each B&J bigmouth for the top floor and the two original Hoffman 45s on the first floor mains. each tee is also where the dry returns take off.

    i just installed a 0-3psi gauge to keep an eye on things and got hardly a flicker during the call for heat. definitely less than .25psi before the thermostat shut it down.

    i'm just using the palm of my hand detector, so i can't be certain what i'm feeling, but i can feel the mains gradually go from cool to hot during a call for heat, and once the ends of the mains are reached, i could feel it start to get pretty hot at the ends of the dry returns too.

    i guess mostly i was just surprised, i had sort of assumed the returns would stay cool or just warm with condensate later in the heat cycle