Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Venting 2-pipe

Trying to save a few bucks and keep things running well with the steam systems in our church.

The church rectory is a two pipe vented system. That’s right- except for a couple of errant“one pipe” radiators, each radiator is dripped to the wet return and has a radiator vent.

Several of the radiators also have traps, suggesting that at some point in the system’s history it was standard two pipe.

There are no main vents (no old traps, either). Adding main vents seems like a no brainer, except that the main piping is spaghetti (see diagram). Given the smallish diameter of the mains and the weird bullheaded t’s and such I’m antsy about creating a situation where one portion of the main is favored over another, or some other weird situation.

Many factors make these calculations messy (the main starts off at 2” but reduces to 1 ¼” in most places) and there are a bunch of runouts involved, but I’ve measured roughly 101’ of main. By divvying up the shared piping, I’m assuming:

Boiler to Drip A = 29% of the total venting needed

Boiler to Drip B = 17% of the total venting needed

Boiler to Drip C = 23% of the total venting needed

Boiler to Drip D = 32% of the total venting needed


· Given the current configuration, how would you vent this system? Size and placement of vents?

· In “as few moves as possible” what changes would you make to the piping in the future?

· Would you recommend removing the guts from the (now useless) radiator traps to, say, ensure they don’t fail closed and force condensate to drain via the (undersized for one-pipe) steam side?


Patrick North


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Installing main vents

    You could put some gorton2's on next to each drip. If you over vent, you will not have the problem of favoring one section over another. A good low pressure gauge will enable you to see when the back-pressure of venting is as close to zero as possible.maybe one on b, and two on each of the others. Make sure the radiator vents are slow, and the steam will fill the mains first before the rads begin to fill.

    What is controlling the boiler-thermostat?--NBC
  • Patrick_North
    Patrick_North Member Posts: 249
    Heavy venting

    So go heavy on the venting and all should be fine?

    Any thoughts out there as to removing bellows etc. from the vestigial traps?


  • Jamie Hall
    Jamie Hall Member Posts: 22,901
    If the traps fail closed

    they would be a nuisance.  In which case you would want to remove the guts of the traps.  However, they usually don't fail closed -- open is much more likely.  And getting into them can sometimes be a bit of a hassle.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
This discussion has been closed.