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Location of Main Vents - Not End of Main or Return

Ps44 Member Posts: 30
I was reading a brochure from
Peerless Boilers and was surprised to see that they said you should not locate the main vents at the end of the main or return since all my main vents are located exactly that way. I was wondering if anyone could enlighten me why the dead men would locate them there and Peerless is saying they shouldn't be. Pictures from brochure above and a main vent below. Any thoughts would be welcome to understand this better.


  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,787
    They say it's to mitigate damage from water hammer, but we don't allow no damn water hammer in our steam mains, now do we? :)
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Jamie Hall
    Jamie Hall Member Posts: 20,488
    It is certainly preferred that they be set back from the end of the main or return, but it makes little difference to the venting -- and as @Hap_Hazzard said, rather forcefully, if things are done correctly there won't be a water hammer threat.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 10,320
    The 90 on the end of the main does add a little protection.
    But they had a take off where the vent should have been, so it was a compromise for that day.

    What you can do to get the protection is remove your vent, add a 6" or more riser with a 90, then a 12" horizontal pipe with another 90, then a riser as space allows for your vent.
    This gives enough restrictions that may help with water hammer.
  • neilc
    neilc Member Posts: 2,087
    what you can do,
    at least with that vent pictured,
    is to raise the vent up on a nipple and coupler, like in the "approved" drawing,
    or 90 or 45 away and add a nipple and same angle, and raise the vent up,
    or even build an antler if you're finding you need more venting capacity.
    you're moving the vent up and away from any condensate water flow at those end of mains.
    known to beat dead horses
    JUGHNE Member Posts: 10,320
    I have mentioned this before, but in case I forgot it I want to tell the story again. ;)

    The WW1 trenches were not a straight line, rather a ziz-zag pattern so any shock waves would not travel that far.....just like water hammer shock.
    EBEBRATT-Ed Member Posts: 13,149
    I strongly agree with raising the vent as high as possible. I would use 45s for any offset as a horizontal pipe could be pitched the wrong way and hold water

    Vents on a tee at the end of the main or dry return if they don't spit water and work ok just raise them and leave them in the same location
  • Ps44
    Ps44 Member Posts: 30
    Sorry I didn't say this but I don't have a water hammer problem or any problem at all so this was definitely done correctly. I was just being curious about the differences. Thanks for all who weighed in.
  • motoguy128
    motoguy128 Member Posts: 394
    I just don’t think it’s an issue unless you have wet steam and hammer issues. The trickle of condensate in most systems should never blast out a vent unless the system is out of whack.

    A 200k boiler output is 160k BTU. That converts to approx. 2.7lbs of water or 0.3 gallons per minute of condensate. Thats a steady trickle. That will fill a pint glass in 22 seconds.
  • neilc
    neilc Member Posts: 2,087
    there is something to be said for leaving well enough alone,

    now this curious cat wants to see the boiler and the near piping,
    to see whether it's a well done pipe job,
    or a situation where a departure from the manual minimums, or better, "still works"
    known to beat dead horses
  • Ps44
    Ps44 Member Posts: 30
    This is an old house, over 100 years, so the near boiler piping was terrible. Having it redone was the first thing we did to manufacturer's exact specifications. Solved most of the problems from day one.
  • ethicalpaul
    ethicalpaul Member Posts: 4,208
    The piping was probably good 100 years ago. It’s the 40 years ago to present stuff you have to watch out for. 

    I assume your boiler isn’t over 100 years old?
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • Ps44
    Ps44 Member Posts: 30
    Yes, that's right. If I remember correctly boiler is about 19 years old but pipes are original except for near boiler piping. We have boiler serviced thoroughly every year and that's worth every penny.