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Main Vent

MikeyG Member Posts: 10
Hi --

I am not a professional but have read both of Dan's books on steam heating.  The attached pics are the main vent on my very small 1 floor -- 4 rad heating system.  It is at the point where the dry return starts to turn downward and appears to be done the way Dan says it shouldn't be -- at the T fitting -- but is on a long nipple.  Is this something I need to change?  (of course, I'd not so this myself but call a qualified steam heating person)  Should it be moved back 15- 18 inches back along that return pipe?  I cannot tell whether that main vent (Hoffman 4A) is even working any longer.  Advice please.  Thanks in advance.



  • kcopp
    kcopp Member Posts: 4,305
    technically ....

    you are correct. But to pull that apart for  15 inches is not needed. If you add a couple of 90's and a new vent you will be fine.
  • MikeyG
    MikeyG Member Posts: 10
    Thanks but a question ...

    Thanks for your response.  So, if you don't mind, please explain how these 90 degree elbows would be positioned on the existing tee.  Thanks again .
  • BobC
    BobC Member Posts: 5,431
    Like this

    This shows how i handled a similar situation on my system, not pretty but it works. Make sure the piping allows any water to flow back to the steam main and return.

    Your main vent looks much to small, replace it with something that has more venting capacity.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • MikeyG
    MikeyG Member Posts: 10
    Type of pipe to use?

    Just so I know whether the plumber I hire knows what he is doing, should he be using black steel pipe for the main vent line and elbows you describe?  If not, what should be used?  Thanks again!
  • Rod
    Rod Posts: 2,067
    edited April 2012
    Main Vents & Antlers

    Hi- The reason for moving the vent back 15 inches is that in some situations steam can push slugs of water down the pipe which slam into the elbow. If the vent is mounted directly on the elbow, this can damage the vent. In your case the vent is mounted well above the elbow and adding a couple of elbows will further protect the vent.  (Water slows down when it goes around corners)  The big thing is to have good drainage away from the vent so that any water that reaches it will immediately drain away.   The Hoffman 4A vent which you have now is pretty small venting capacity wise.  A Gorton #1 would give you 3 times more venting capacity. A Gorton #2 about 10 times more venting capacity and a Hoffman #75 about 5 times the venting capacity.   Since you have a small system maybe just replacing the 4A with one or two  Gorton #1(s) would be sufficient. Put it (them) on an "antler "  (see attached diagram) and if you want to add more venting it is easy to just add to the tee. Unlike radiators you can't over vent on main vents.

       Hoffman and Gorton Vents are available from a local heating supplier or on the internet at Pex Supply.  http://www.pexsupply.com/

    Testing vents-  DO NOT test vent operation with your bare hands! Live steam can give you a very bad burn!   The best way I have found is to use a strip of newspaper about a foot long and hold it near the vent opening. The air flowing out the vent opening will move the paper and when the vent closes, the movement will stop.

    Black pipe is best as the zinc on galvanized pipe can flake off and possibly plug the vent hole which is pretty small. Changing the vents is fairly easy so you could probably do this yourself if you are inclined.

    - Rod
  • MikeyG
    MikeyG Member Posts: 10
    Thanks for you very detailed answer!

    Many thanks for your comprehensive response.  I will definitely have the pipes altered as suggested and change the main vent to a Gorton #2 for now and see whether that helps the heat to move to the rads faster.  If it is still slow I will try that antler approach.
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