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is an extra main vent - not at end - a bad thing?

I've got a three story six unit building, built in 1920, originally heated with coal. It's a one pipe system, now with natural gas. It has with two main runs. One is about 35 or 40 feet. The other splits off this first, goes about 100 feet in one direction, then loops back another 50 feet or so before it hits the main vent. There's a sealed up T about 40 feet into the first 100 feet of main run. I'm thinking of putting a second main valve on this T. This would be about half way through the whole run. Could doing this harm anything? Thanks in advance for sharing any info you may have.


  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    It will speed up the radiators that are before it and keep the ones after, some what behind. The goal is to heat all the rads at about the same time. Can you branch your vent location and add more vents at the end of the runs?
  • ttekushan
    ttekushan Member Posts: 22
    I'm not sure that

    it is really detrimental to balance. the air scoots through and when steam hits it, it closes. I see what you mean though. The main vents at an effectively decreasing rate as the steam advances through that main. But I cut my teeth on a large two pipe system where the long main had 3 drip stations, i.e., the main was dripped and vented through F&T traps into the dry return. This set-up was essentially vented at intervals along the main.
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    Im sure it would speed up the venting, I guess it would depend on where the hot and cold rooms are and where the stat is. If you accelorate the heating in the stat location you could compound the problem in the end rooms.
  • I like to have all venting capacity

    at the ends of the mains. This makes sure all rads have equal access to the steam. The exception is in large, complicated piping systems where sometimes the venting must occur in stages.

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