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Mechanical Vent and/or Proper Venting?

steam2pipe Member Posts: 59
In 2013, one 'mechanical vent' was installed (actually replaced) under a kitchen sink that is attached to another kitchen sink (through the wall) because these 2 housing units on the 1st floor share the same piping as their units are adjacent to each other. The plumber installed it because one of these sinks was backing up into the basement's sink directly below. Their units are on the 1st floor of a 3 floor level old 1860 historic house. The basement unit's kitchen sink is directly below and 3 years ago (2016) when a bucket of sudsy water was dumped into the 1st floor sink above the basement's sink, it overflowed again into the basement's sink. The drain people snaked the units involved and the main drain, checked that the mechanical vent was ok and now 3 years later the problem has reoccurred. 3 years ago the drain company rep told us that the 'mechanical vent' , while still in tact, was not legal any longer and the sinks needed 'proper venting' from the roof. This was reported but management didn't do anything. Now 3 years later, management just wants to snake the main drain (not the 3 units affected) and are not addressing the 'mechanical vent' issue. I am not a plumber but I am seeking to understand how it works as we are in the unit most affected by the recurring deluge into our sink. If someone can help with some thoughts on the following questions, I would really appreciate it, so we can prevent this from reoccurring.
1) Are mechanical vents the same as AAV vents? Are AAV vents a possible solution to this? or are they illegal, too?
2) What does 'venting through the roof' actually mean? The two units which share the wall and the mechanical vent have 2 other units directly above them. The roof is on the 3rd floor.
3) What would you recommend that I tell management?
4) Should I call inspectional services? The stuff that overflows into the sink might be a health code violation.


  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    The aav is a mechanical vent, and stands for "automatic air vent", and It depends on your jurisdiction whether it is legal or not . You would have to check with your local plumbing department. It is not legal in Alaska, but is legal in some places.
    Venting through the roof means that the vent pipe does not terminate in a mechanical vent, but continues on up and out the roof.
    My recommendation would be to just have the drain snaked out again. I seriously doubt the vent has anything to do with the drain backing up. My experience says the drain is backed up because it has kitchen sinks draining in to it and is most likely plugged with grease.
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    I'm with @rick in Alaska on this one. The automatic air vent may or may not be legal in your area; you would have to check with the plumbing inspector in your jurisdiction. Be that as it may, poor venting almost never causes a drain back up such as you describe; that's almost always the drain being clogged,

    Now it may be in addition to the drains being clogged from grease -- which, incidentally, should never go down the drain -- or hair etc. that the drains in question are simply too small and should be replaced. It may also be that you have inadequate or improper venting, but that's a different problem. It is possible that your management is aware of this and is reluctant to have an inspector evaluate the plumbing...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • steam2pipe
    steam2pipe Member Posts: 59
    Thanks, Jaime and Rick, for your comments on this. The drains may be too small, and we may also have inadequate venting. Management is having the main drain and the 3 unit sinks snaked on Saturday so that is good news for us. I have asked for a plumber to check the mechanical vent that is there to see if it is still working. If it is not, and there is not adequate venting, that may be another problem as you have noted. Thanks again for all your help.