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Hi, I've had an recurring (but occasional) problem with spitting and dribbling vents. It seems to happen especially but not only during cold spells.Since I took over the building some 13 years ago I've tried to eliminate problem after problem. At this stage all radiators are properly pitched, improperly pitched piping has been corrected or eliminated and vents have been replaced as necessary. The system is almost silent and, for the most part, works well.

I recently had a local steam system expert come and diagnose the issue. He saw two issues.
First, an oversized boiler. It's a Burnham that was originally used with oil (from 2003) and then switched to gas in 2009.
Second, undersized risers throughout the 4-storey building. Eight risers in total. Four are 1 1/4" and 4 are only 1".
(If the diagnosis is correct the it would appear the Dead Men made an uncharacteristic error...?)
Strangely, on the top floor the risers have a reducer coupling and the riser pipe size increases to 2" until it stops just below the ceiling. The local expert advised eliminating these sections and replacing them with a 1' long pipe 3/4" ID, topped with a master vent.

He also recommended adding vents to the mains and the top of the risers and putting slower venting air vents on the radiators. And adding a vaporstat, which is on order already.
I'd be grateful for any second opinions on all of this and about whether downsizing the boiler is possible.
Or actions that can be taken to stop the spitting vents etc.

Thanks in advance for any thoughts on all this.



  • neilc
    neilc Member Posts: 2,707
    what pressure are you running now?
    how is the boiler piping? pictures?
    with the work you have already done, the piping work,
    have you skimmed? reskimmed the boiler?
    known to beat dead horses
  • Gobbaloon
    Gobbaloon Member Posts: 6
    Think pressure is somewhere around 8oz.
    The boiler has not been skimmed in at least a decade. But no evidence in gauge glass of surging/foaming.
    Here are some pictures.
  • neilc
    neilc Member Posts: 2,707
    That's far too large a boiler for 1 riser, You need at least the second, and likely the 3rd. This is definately sending water up in the steam = wet steam and spitty vents.
    Download or obtain the manual and be sure the risers are aligned first on the header, then the system take offs, then your equalizer, It's like that now, but missing the 2 boiler risers.
    If you are operating at 8oz you either have a well matched boiler to building EDR, or, gulp, a leak.
    Do you know your building EDR ?
    Does this boiler cycle during a call for heat?
    Add a low range gage there somewhere, 0-3, or 0-5, hard to tell 8oz on the 30# gage.
    If you're seeing higher pressures and cycling on the Ptrol,
    if that's your operating Ptrol, you have room to adjust it down some, set the main to 1.5, and the Diff to 1(one). I see the main set just above 2 right now, and diff at 2.
    Running higher pressures isn't helping the wet steam spitting vents situation, and is also using extra fuel.
    Those system takeoffs rise straight up thru the building to the top?
    then yes,, they want to be main vented, up top.
    known to beat dead horses
  • neilc
    neilc Member Posts: 2,707
    rereading your original post,
    more questions,
    1 pipe or 2 pipe radiators ?
    rad picture ?
    Is it 8 risers?
    or 4 up(1 1/4") and 4 returns(1") ?
    picture of the top of riser where it expands up to 2 "

    If your steam expert didn't mention the boiler risers and header then maybe you need a better steam expert.

    known to beat dead horses
  • Steamhead
    Steamhead Member Posts: 16,893
    What model Burnham is that? Burner looks like it might be a Midco, which model?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Gobbaloon
    Gobbaloon Member Posts: 6
    Hi, sorry, I should have specified that it is a one-pipe system. And yes, there are 8 risers.
    Burnham is V904 A
    The burner is indeed Midco. Model RE 4700 BA.
    Attached are some pics of typical radiator. Plus reducer at 4th floor where riser expands to 2" for it's last 8-9'.

    Best, Frank

    JUGHNE Member Posts: 11,075
    I would say the pipe increaser from 1 -2" is to add more radiation to the room.
    I would keep it in place as just from looking at a big boiler you would not want to eliminate any EDR from the system.
    It can probably be down fired only so much
  • Gobbaloon
    Gobbaloon Member Posts: 6
    Jughne, I think the recommendation to remove that 2" section of pipe at the top of the riser was based on the idea that as it's a riser it's being vented quickly. So when the steam hits it, you suddenly have a small downward rush of condensate as steam is still trying to fill the radiators and that this might be a partial cause of water being forced into the radiators and through some of the vents.
    I understand what you're saying that those sections were placed there to increase radiation on the 4th floor. But maybe a larger radiator (with it's slow venting) would not cause the same sudden backwash of condensate but a gentler dribble. (I know I'm out of my depth here so maybe my visualization of what's happening is way off.) Thanks.