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Main vent location

Ive got a job where there are no main vents on the 2 mains. The long main is 3 inch and is approx 65 feet long and the short main is 2 inch and about 35 feet long. The long main had no provision for a main vent. Although not the best location, I installed a tee at the end of a 6 foot dry return at the exit of a crawlspace before it dropped down to a wet return. I will pipe the vents up and over to prevent condensate hitting the vents. (see attached photo, please ignore the hoffman vent the 2 Big Mouths for that are on order). The short main I am not so sure about. It ends in the back of a different crawspace and there is a 2x3/4 tee before it bends back into a dry return that runs all the way to the boiler. The issue is the tee is turned horizonal. In such a tough spot trying to repipe it so its facing up is near impossible. Is it ok to come out of the tee horizonally with a nipple then 90 up and attach the Big Mouth? If that isnt ideal, I could always attatch 2 Big Mouths at the end of the dry return back by by the boiler (about 70 feet from beginning of main to end of dry return at boiler). Just wondering what the best option is. Thanks


  • Fred
    Fred Member Posts: 8,542
    Either way will work, if you can get the vent up high enough to prevent dirt from washing up into the vent. Ideally, putting the vents at the end of the dry return, near the boiler will be a lot easier to maintain them and/or see them if they ever leak. Is that worth the cost of another vent for the added distance?
  • upstateben
    upstateben Member Posts: 33
    @Fred the only other thing I was worried about and Im not sure if it even matters is I feel like my "a" dimension at the end of that dry return is a little small. I measured 23 inches. There has not been any problems but I am wondering if placing a main vent there may cause problems since I am going to completely fill the dry return with steam at the startup of every cycle?
  • Fred
    Fred Member Posts: 8,542
    You really don't need to vent the dry return anyway. If you are more comfortable putting it in that crawl space, it saves you a vent too.