Air Return Issue

[edee_em]

I was removing some aspenite (pre-osb) subflooring to prep for a hardwood install in an upstairs bedroom of a 2 storey home with basement. I got to the wall where the return air vent is and I was baffled by what I saw.

The vent on the wall, itself, is not connected to anything. That's not a huge surprise as the builder used the stud bays as return ducting. However, the other returns in the house do continue through the stud bays down to the first floor and on into the basement where the hvac ducting exists.

This one doesn't do that. There is a doorway (on first floor) directly below the spot where the return was placed so they couldn't go straight down. I checked to the left (looking at the vent wall) and there is a "duct" in the floor about 2-2 1/2 feet away. Let's call that one Duct 1. We have to call that one Duct 1 because I found another stud bay return duct (Duct 2) a joist bay away from where the return is. First question is why are there two returns?

Also, with a joist in the way, I can't see any way for the air to be drawn down into that stud bay vent (Duct 2). I checked both ducts and they both go down to the basement. I did find a largish piece of vapour barrier in Duct 1. Was it put there on purpose? I took it out as I'm not familiar with that high level of duct design

In the basement I can see a sheet metal "cap" of some kind closing up the joist bay to create the duct. This is the Duct 1. Right beside it I can see the joist bay covered with sheet metal to create the duct. This is Duct 2. This duct is the one that goes to the furnace return. The other (Duct 1) does not as it is in a staircase wall and can't get across the stairs. Duct 1 has to join into Duct 2, somehow. I haven't taken down the sheet metal to see but I know that there is (at least I think it's still there) a joist between these two, in the basement.

I also checked the draw on the two ducts. With the fan on Duct 1 did not draw as well as Duct 2. I closed off Duct 2 and Duct 1 drew a lot better. So, the next question is, why do I have two returns, do i need to have two returns in this room and what would the purpose of a return air duct in the floor of one room of a house full of rooms be? I would like to know if I can close off Duct 2 permanently without issue. My hope is that there was an error made and I can fix it.

Would appreciate any help with both explaining what they did and how to solve it. Thanks

[Hgye]

It might be clearer if you remove the joist lining. You may find the joist drilled full of holes, who knows. There is a saying in hvac that says "You cannot have too much return air". If the extra return is providing some air flow, I would leave it like it was.

[edee_em]

Thanks Hgye. I will have to take a look to see what's going on.

Sounds like you agree that the two vents are connected, somehow (God I hope they didn't just drill out the joist holding up a house). If they are, is it really providing more air return? My logic (not very good at the best of times and based on 0 HVAC training or experience) is that two returns would be returning at 50% each since they are joined. I'd rather have one return at 100% returning air from the room rather than the floor. Does that make sense to you?