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location of main vents

I am wondering about the location of my steam main vents. The house is 1927, 7 cast iron radiators, new W-M EG35 put in a year ago. I just stripped and repainted all the cast iron, and will soon be replacing all the radiator vents, but after learning so much from the books and from the wall, I still don't know if my existing vents are located properly.

From the diagram attached, you can see I have 2" pipe rising into the header, and two 2" mains running out from there. After the 6 risers/runouts branch off, the 2" line reduces to a 1.25" return, about a foot below the supply mains. This is where I would expect to find the main vents (represented by a ? on the diagram), but instead, they are both above the boiler (represented by G1 since they're both gorton 1's), at the end of where each return drops down to ground level before going into the hartford loop.

I understand that "where there is air there cannot be steam", so to fill my mains, steam pushes all the way down the mains and back the returns, pushing out the air, before the main vents close and steam will push out the risers/runouts.

Is this a big deal, enough to warrant adding new vents where 2" pipe reduces to 1.25" (at the question mark)? Or with my relatively short mains (6 and 17 feet), is it not worth the cost of getting the plumber do new taps?

A big thank you in advance for your help!


  • jpf321
    jpf321 Member Posts: 1,568
    edited October 2010
    i think ....

    i think that what you have is reasonable. it will take a little longer for the steam to close the vents at the current location, but not a significant amount longer. if you move the vents, i'm not sure of the repercussions of having an air cushion between your last vent and the wet return. if you were to move them, in theory the steam would hit an air cushion and then start heading up to the rads slightly sooner. personally, i think you are fine as long as you are well vented past the last rad on each branch.

    EDIT: FYI, I plugged your numbers into my spreadsheet (linked below in signature) .. on the 36ft side, you should have 3 pieces of Gorton #1 (or 1 pieces of #2 if it's easier) and the 15ft side you should have 2 pieces of Gorton #1. Assuming a desired time to vent of 1min at 1oz.
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
  • Brad White
    Brad White Member Posts: 2,398
    I would also

    pull those vents back from the end-of-main tees by about a foot. (The classic standard is 15 inches, but that really is the sum of a 12 inch nipple plus the fittings, you get the idea.)

    If you install the vents on a dead-end tee like that, a slug of water will go up into the vent as easy as down, and damage the vent.

    If you cannot reasonably cut in a new tee, can you put in a "back-offset" by about as much and rise the vent as high as you can?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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