Results 1 to 8 of 8
  1. #1
    Join Date
    May 2019
    Location
    Fishers, IN
    Posts
    4
    Post Likes

    question on b-vent and cold air return in same wall cavity acting as a "chase"

    Hello,

    In my home there is an area between two walls on the second level that contains b-vent from the gas furnace and also a galvanized cold air return duct both of which are running from the first level furnace up to the attic and so pass behind this wall on the second level. There is the outside wall, a space, and then an inside wall forming this cavity. I am in the process of remodeling the shower that is on the interior side of that inside wall which is why I now have access to the cavity behind the wall to see this.

    I don't know enough to know if this is a common situation or if there would be reason to be concerned so I wanted to ask the pros! Would you generally be fine with a ducted cold air return and b-vent in the same space between walls or would you expect those to have a divider or separator between them so that they are not open to each other behind the wall?

    I'll try to attach a sketch of the layout looking from the top down here: Name:  IMG_20190519_135548.jpg
Views: 86
Size:  72.9 KB

    The sketch shows the passage the return and b-vent are in. The exterior wall is on the top immediately adjacent to the duct and vent, and then interior wall is immediately adjacent to them on the bottom. Between the b-vent and the duct is some open space between the two walls.

    Thanks!

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    39,766
    Post Likes
    B-vent is not air tight so any negative pressure on it could suck flue gases out of it. Could be dangerous.

  3. #3
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    8,560
    Post Likes
    It looks like in the drawing that the two are separated meaning that air going around the B-vent is not going into the return duct. If the B-vent is going through a galvanized plate it could be an old fire stop. The main concern would be that air being pulled into the return is not going around the pipe. If it is that is a concern as Baldloonie said, if there is a joint in the b-vent in that space it is even more of a concern as the joint will be more apt to leak fumes than the 2 layers of pipe.

  4. #4
    Join Date
    May 2019
    Location
    Fishers, IN
    Posts
    4
    Post Likes
    Thread Starter
    Thanks you both, that helps a lot!

    They are open to each other in the cavity, the line that curves off of the main return is actually a branch off of the return down lower for a room on the first floor (it's a tri-level, so low on that wall is the back of another room). Additionally, the only way air can get into that cavity is from the left side of the drawing where air can enter the passage from between levels. (there is an opening at the base of that wall between studs where some plumbing runs through.)

    Give that, if there was a leak in the return it would draw air from that left side over the b-vent which sounds exactly like what you are both saying would be concerning.

    Thanks for helping me sanity check that!

  5. #5
    Join Date
    May 2019
    Location
    Fishers, IN
    Posts
    4
    Post Likes
    Thread Starter
    Yikes, that is exactly what made this suspect to me. Thanks for helping me sanity check this!! The only opening in the cavity is from the left side of the drawing there there is a plumbing access at the base of the wall, so if the return were to leak it would draw air in over the b-vent (and there is a joint in the b-vent in there as well.) I really appreciate the professional opinion, thanks!

    (sorry, I double posted because I was trying to respond to the replies individually lol. I'll get the hang of this yet!)

  6. #6
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    8,560
    Post Likes
    Quote Originally Posted by rreinhardt View Post
    Thanks you both, that helps a lot!

    They are open to each other in the cavity, the line that curves off of the main return is actually a branch off of the return down lower for a room on the first floor (it's a tri-level, so low on that wall is the back of another room). Additionally, the only way air can get into that cavity is from the left side of the drawing where air can enter the passage from between levels. (there is an opening at the base of that wall between studs where some plumbing runs through.)

    Give that, if there was a leak in the return it would draw air from that left side over the b-vent which sounds exactly like what you are both saying would be concerning.

    Thanks for helping me sanity check that!
    When you say if the return was to leak says to me that you don't have an issue. The b-vent and return duct can run in the same space. The problem comes from when the space is used instead of return duct. So in your drawing if there was a return opening on the left and air went from that opening across the b-vent and directly into the return duct. As long as you don't have that direct connection it is not a problem.

  7. #7
    Join Date
    May 2019
    Location
    Fishers, IN
    Posts
    4
    Post Likes
    Thread Starter
    Quote Originally Posted by BNME8EZ View Post
    When you say if the return was to leak says to me that you don't have an issue. The b-vent and return duct can run in the same space. The problem comes from when the space is used instead of return duct. So in your drawing if there was a return opening on the left and air went from that opening across the b-vent and directly into the return duct. As long as you don't have that direct connection it is not a problem.
    Oh!!! Thanks so much for that clarification, that is it exactly. The cold air return duct is not open to the cavity in any way but just passes through on it's way from the attic to the lower level. So it's adjacent to the b-vent in there but it has no openings into the cavity.

  8. #8
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    8,560
    Post Likes
    Perfect, glad we got that cleared up for you.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •