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Main vent

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georgearoush
georgearoush Member Posts: 37
in Strictly Steam

In my two-pipe system, there are three vents. Two of them are located at the very end of the main supply pipes coming off the boiler (one is ~30 feet, the other ~20 feet), and they look like this:

20260228_105619.jpg

The third vent is located on the dry return line, and it looks like this:

20260228_105735.jpg

Both vents are very old and need to be replaced, but I’m not sure what type or size I should get. Do you have any recommendations?

Also, I noticed the following modification on the dry return pipe. Do you know why this might have been done?

20260228_105943.jpg

Comments

  • mattmia2
    mattmia2 Member Posts: 16,890

    the water seal looks like they have stem getting in to the returns for some reason and instead of fixing it they put that water seal in. it should be keeping that emitter from venting and heating

  • Jamie Hall
    Jamie Hall Member Posts: 27,395
    https://forum.heatinghelp.com/discussion/comment/1890215#Comment_1890215

    I love the shark bite. And it looks like the pipe to the right has a reverse slope…

    Check the trap on the radiator to which that is connected. I'd bet that it's failed.

    I'm not sure that it would keep the associated emitter from heating, at least some — if the system pressure is also excessive. But it ain't right.

    You might also want to check for the system main vent on the dry return before it drops to the boiler. That is the primary main vent for the system, and if it's missing or failed the system won't heat as well or as evenly as it should.

    The other two vents shown are woefully inadequate. Try putting a Gorton #1 or preferably #2 on them.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • georgearoush
    georgearoush Member Posts: 37
    https://forum.heatinghelp.com/discussion/comment/1890217#Comment_1890217

    From the first picture I shared, the existing air vent’s screw-in part is not a Gorton, it is smaller. Do you have any idea what type of vent this might be?

  • mattmia2
    mattmia2 Member Posts: 16,890

    dole? they are basically radiator vents, way too small for main vents on a gas or oil boiler.

  • ethicalpaul
    ethicalpaul Member Posts: 8,850

    Do you have any idea what type of vent this might be?

    Yes, it's inadequate

    NJ Steam Homeowner.
    See my sight glass boiler videos: https://bit.ly/3sZW1el

    mattmia2bburd
  • georgearoush
    georgearoush Member Posts: 37

    My question isn’t about the vent’s capacity or size, but rather the type, specifically the threaded connection, so I know what to purchase. Please see the picture below.

    image.png
  • Captain Who
    Captain Who Member Posts: 883

    Measure the outer diameter (O.D.) and look it up in this chart:

    https://usaindustries.com/piping-isolation-testing-products/pipe-schedule-chart/

    I'm going to guess that the reducer is a 3/8 to 1/2 reducer which would mean the vent is 1/2 NPT.

  • Jamie Hall
    Jamie Hall Member Posts: 27,395

    At rick oif the obvious — you can purchase reducers or expander bushings of almost anything to almost anything. The size of the thread connection is almost irrelevant.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,228

    looks like 1/4 x 3/8 or 1/2 to me but pictures lie

  • Steamhead
    Steamhead Member Posts: 18,525

    I think that vent is a Hoffman #43, which has a 1/4" thread. The similar Hoffman #41 has a 1/8" thread. Both are designed for use with convectors and vent about the same as a Hoffman #40 radiator vent, which is to say, way too small for a main.

    The dry return vent is a "USAV" which is actually made in China, and is just as bad.

    So, @georgearoush , here is what I would do to start out, using Gorton vents:

    For the longer main, get a #D with 1/4" threads:

    https://www.supplyhouse.com/Gorton-GDS4-Gorton-No-D-1-4-Straight-Vapor-Equalizing-Valve-3538000-p

    and for the shorter one, a #C:

    https://www.supplyhouse.com/Gorton-GCS4-Gorton-No-C-1-4-Straight-Vapor-Equalizing-Valve-3535000-p

    For the dry return, use a standard #1:

    https://www.supplyhouse.com/Gorton-G14-Gorton-No-1-3-4-x-1-2-Air-Eliminator-Main-Vent-Valve-3522000-p

    Note that the #D and the #1 both vent at pretty much the same rate.

    See how this does and get back to us. Also, can we see some pics of a couple radiators, to see how they are piped?

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting

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