The Return Duct to Nowhere....

fpgoaOctober 13, 2011

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.

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heatseeker

I would see if there is a way to put in a second return into the ceiling on the second floor might be worth looking into.

    Bookmark   October 14, 2011 at 10:54AM
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energy_rater_la

your hvac company that has seen you situation has
a better view of what is going on than we do...just
saying...but

"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."

if it truly is abandoned then cap it off as close to the
plenum as possible. insuate the cap (sheetmetal) and mastic seal the cap. fyi all ducts should be mastic sealed.

"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."

hard to say without seeing the duct & surrounding areas.
your assumption that the duct sucking in non filtered non
conditioned air is right.

'Third question, should I insulate this space while I have it open? '
is this an exterior wall?
I always insulate. Realistically I know that insulating one area of a wall when the rest of the wall may not have any insulation ..doesn't do a whole lot. its just the way I work. always air seal, always insulate.

best of luck.

    Bookmark   October 15, 2011 at 11:01AM
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countryboymo

I know someone who had the same situation and the space could be used for wire runs to the attic so he put conduit from the basement to the attic and then sealed the space and blew it full of insulation and ran a coax for an antenna in the attic and sealed it and the remaining conduits.

    Bookmark   October 15, 2011 at 1:01PM
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mike_home

Is it possible the upstair bathroom was renovated by a previous owner and during the renovation someone decided to remove the return vent in the bathroom?

Most duct systems have insufficient return air. It would be nice if you could make use of this return. I am not sure capping the return is a good idea. Even though it is buried in a wall cavitiy, it is still pulling in some amount of air back to your furnace.

Can you temporarily block the return duct and see how it affects the performance of your supply vents?

    Bookmark   October 15, 2011 at 1:09PM
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fpgoa

Thanks for all the responses and ideas. To fill in further, the bathroom is original (pink tiles, tub and all), it never was moved or remodeled. The duct in question stops 2 inches under the subfloor to the bathroom and never went into the room. The wall it is located in is an interior wall. You literally can see the wires for the kitchen stove area lighting and the back of the wall from the fridge from the family room side. The real in use return duct which has a vent in the family room is a foot away. This duct goes into the basement where it meets the return system next to that duct. The other return side has a duct in the living room (split level between first and second floor) and there are the two small return vents in the stair side of the linen closet on the second floor before it ends inches from the attic crawl space.
I could potentially see running some sort of return into the master bedroom on second floor since this duct is literally 4 feet away in the exposed area. The other two rooms which also have no return are more than 10 feet away and the floors are closed up and have old hardwood.
Even though our HVAC is less than a year old the upstairs (especially) the two rooms are not near the other rooms temps.

    Bookmark   October 15, 2011 at 2:04PM
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veesubotee

Many codes prohibit returns in bathrooms (and kitchens).

V

    Bookmark   October 16, 2011 at 9:01AM
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fpgoa

I don't think anyone would put it in bathroom or kitchen. I am speaking about one of the bedrooms.

    Bookmark   October 16, 2011 at 11:24AM
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