The Return Duct to Nowhere....
I originally posted this in the Old House forum but with further research I believe I may need to do something with this duct.
Here is the original post:
Longer story shortened. We have a 50+ year old suburban house in NJ and we recently had a pipe break in our second floor bathroom. The remediation crew ripped down a family room wall on the first floor since it was soaked in the break.
In the wall, I found what appears to be a functioning, extra return duct (6 x 18, extending from the wall of our basement and reaching up underneath the floor of the bathroom on the second floor, only stopping short of the second floor bathroom floor by a half of foot or so). The bottom of the duct returns to our big return trunk in the basement (right before the A/C unit) through a cinderblock wall and the top cuts off without any kind of capper and obviously it doesn't extend through the bathroom or family room wall, it is just there sucking in non-living space air for the last 50 years.
First question, what should be done with this?
I assume I should cap it off as low as possible since I cannot remove it from the cinderblock basement wall without leaving a hole. My HVAC contractor who replaced our AC last year said he can cap it with sheet metal.
Second question, is there any purpose to this duct? I assume sucking in non-heated or non-AC air only makes the HVAC system work harder to maintain the appropriate air temp in the living areas since this area is not all insulated.
Third question, should I insulate this space while I have it open?
This is a few foot thick empty space between the back wall of my kitchen and family room, the top side of the back wall of my laundry side of an unfinished basement (split level house) and bottom area under my newly busted up bathroom on the second floor. The 50 year old tile was all ripped up due to the leak so for the time being I can look through the subfloor upstairs into this space and into a foot or so of my family room via the broken wall down there.
I have recently spoken with a neighbor who has a similar style house and he believes this duct was supposed to reach the second floor.
I looked around my house more and the only return vents (two stuck into a small cavity 5 feet and 1 foot up on the wall) appear to be on the stair side of a linen closet on the second floor. My master bedroom (13 X 13) and two other bedrooms upstairs(9 X 10)(10x14) do not have anything but supply vents. If I were to extend the return duct straight up it would be under the bathroom vanity area, obviously not the optimal place for a return.
I am in no way an expert but can it be that they just simply didn't complete the ductwork in 1958? While the wall is still open should I try to run at least one return vent from this duct into a bedroom or two? I have hardwood floors so I don't know if I want to bust up too much to do this.
Any recommendations are welcome.