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Adding main vent! Two options (I think...)

grye Member Posts: 88
Hi There. My main venting isn't adequate on my 1 pipe steam system. I have a vent on one side of the main, my boiler in the middle but no vent on the other.

The problem is, on this side, there's no room between the last run and the vertical return. Maybe a 6-8 nipple. Not enough room for however many recommended inches before the return. I know this isn't ideal, but I've talked to a few respected steam heads and learned the show (vent) must go on.

So it seems I have two options (but feel free to add others).

1. Remove the elbow between the horizontal main and vertical return and replace with one with a vent on top. I've seen photos of this before. Is this a part? Or is the top of the elbow tapped?

2. Tap as high as possible on the vertical return, add a 90* and then a vent. Is it difficult to tap a pipe? Never done it before.

Been waiting for the warm weather to come around before tackling this. Hoping to get this system balanced for next year (this year was a nightmare).


  • Jamie Hall
    Jamie Hall Member Posts: 21,115
    Either approach will work. If you can get at it, the easiest approach is to take the elbow off, substitute a T, and hook the vent into the top end of the crossbar (the bottom end goes to the drip, of course). Set the vent as high as possible above the T.

    Tapping a pipe isn't all that hard, but it may be difficult on a smallish pipe, and it takes some experience. Not at all sure I'd try it on that application for my first try!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 1Matthias
    1Matthias Member Posts: 148
    Two questions. Is the radiator on that takeoff on the first or second floor? Second, in the photo on the reddit post, it looks like the ceiling is awfully close to the pipes. Would it be feasible to cut a hole in the ceiling for a vent?
  • grye
    grye Member Posts: 88
    The radiator on that takeoff is on the first floor in the living room. Can't vent there.

    I believe I could cut into the ceiling and get a little more clearance if needed. For the T application I'm assuming you mean?
  • 1Matthias
    1Matthias Member Posts: 148
    My thought would be to go with option 1, with the vent as high and as far back from the end of the main as possible. Tapping into the side of a pipe can go ok, but for the size tap you would need for a meaningfully sized vent, it would probably be easier to go with option 1.
  • Fred
    Fred Member Posts: 8,541
    Go with option #1. Ideally you want the vent to be 15" or so from the end of the main but II bet there are more of us here who have them at the end, on a Tee than who actually have them 15" back. As long as your pressure is low and you don't have any water hammer, you'll be fine.