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main air vents are on the dry return?? ok??

First thanks for your reply on copper piping. I spent this weekend opening my entire ceiling looking for the air vents on the main pipe..none to be found.. I only have two air vents on each of the dry returns. is this normal?? I find that my boiler is cycling every 5 minutes, and i read that if it is less than 20 minutes... this is bad. before balancing my radiators, I want to make sure that i am getting proper venting on the mains.. any advice would be appreciated.. putting my ceiling back together now..


  • venting questions

    if you have dry returns, then that is the right place for the vents, when protected from water-hammer. some systems have no dry returns, and are known as counter-flow systems, because the condensate does not flow in the same direction as the steam [all the way to dry returns], just back against the steam flow.

    probably your present main vent location is correct, and just needs improvement. remember, you can never have too much venting, especially if you are going to close the area in.

    others here are more qualified to advise on the correct number of gorton #2 vents you may need. just measure your mains, from boiler to dry return, and they will come up with the recommendations--nbc
  • Main Vents

    Main vents can be either on the Steam Main(s)  or the Dry Return Mains(s) It may depend on whether the system is one pipe or two pipe steam. In some cases you should have a vent on both.  Let us know the size (diameter) and the length of each steam main and we can tell you the size of vent you need. Measure the whole distance from the boiler riser to the vent . Are there any marking on the vents you have now?

    While you have the ceiling open you might want to make a sketch and some measurements.

    Trace out the pipe to the radiators and mark that on the sketch. You'll find it handy for future reference.

    Cycling-  There isn't any "thumb rule" as to length of cycling as there are a lot of things that can affect cycling time.  Inadequate venting is one of them. One of the things you will want to do is to time you system. Make a list of how long it takes to take steam after the bu8rner has been started with the boiler cold. How long it takes for the steam to reach the main vents and how long it takes for steam to reach each radiator.  You can tell this by feeling the pipes as they will get warm when steam first reaches them. Be careful! Steam pipes do get quite hot and can burn you!   Once you have a list of the times it takes for steam to reach the main vents, radiators etc. you will then be able to time them again after you have made a change to your system and that will tell you whether your change is beneficial or not. - Rod
  • jpf321
    jpf321 Member Posts: 1,568
    you can also ...

    try using the venting Excel sheet linked in my signature to determine your venting needs. you need to measure both the LENGTH and DIAMETER of your mains.

    For example, (30ft @ 2-1/2in) + (20ft @ 1-1/2")
    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
  • Jamie Hall
    Jamie Hall Member Posts: 21,568
    Vents on dry returns

    are not only OK, but if you have dry returns... you have to have vents on them!  Otherwise, how does the air get out of them if and when it needs to?  Most vapour systems had that sort of arrangement, and many many two pipe systems.  Most one pipe systems did not -- since they didn't really have returns.

    In many two pipe and vapour systems, the only vents on the whole system were on the dry returns near the boiler, where they drop into the boiler wet return piping.  In some vapour systems, this was a very necessary part of the design.

    As NBS notes, just make sure you have enough venting...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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