Air return issue?

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Old 05-22-20, 05:10 PM
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Air return issue?

I don't even know where to start with this one. 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 itself is not connected to anything. That's not a huge surprise as the builder used the stud bays as return ducting. However, others I have seen do continue through the stud bays down to the first floor and on into the basement where the hvac ducting exists.
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This one doesn't do that. I checked to the left (looking at the vent wall) and there is a "hole" in the floor about 2-2 1/2 feet away but there is the main staircase there and I don't recall seeing any connection to the hvac in the basement from that spot. I looked elsewhere and found a stud bay duct a joist bay away and in a first floor wall perpendicular to the wall where the return is. With a joist in the way, I can't see any way for the air to be drawn down into that stud bay vent.

Would appreciate any help with both explaining what they did and how to solve it if it needs solving. Thanks
 
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Old 05-22-20, 07:02 PM
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Might be another return air path, turn on the fan and use something (smoke) to see if the return actually draws air.
 
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Old 05-22-20, 11:32 PM
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Thanks 57TinkerMan. I used a tissue and the draw from the duct labeled "most likely return duct" was definitely there whereas the other didn't move the tissue at all. I blocked up the "good" return and the there still wasn't any draw from the other.
 
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Old 05-23-20, 07:57 AM
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If the room shown in the picture is where you need the R/A the easiest thing to do would be to install a floor return grille. You can install it anywhere in the joist space left or right to minimize its visual impact as long as you have a direct path to the system return.
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Old 05-24-20, 02:37 PM
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Quick update: Found a huge piece of scrap vapour barrier tucked into the return vent on the left side. Took that out and checked it with candle and lighter and there is a definite draw on the right side vent but not so much on the left side return. Makes sense as they are both tied into the same return path to the return air trunk of the furnace. I tried blocking off the vent on the right and that improved the draw on the left side return.

My question, at this point, is why would they put in two returns (okay, let's say it was in error)? So the question really becomes, do you think it would be okay to block off the return vent on the right as it is obviously not drawing any air from the room?
 

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Old 05-24-20, 08:30 PM
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Since the "right" return air doesn't serve that room or any other you can block it off. Your system will operate as it always has with a slight improvement from you removing the plastic from the other return. That said, I am always reluctant to eliminate return air, many systems installed in homes have deficient return air ducting. Turn on your fan, block the return with cardboard or similar, have someone open and close the cardboard (slowly) while you feel a nearby supply duct. If you don't have a significant change in supply air closing the return probably is not an issue. If the airflow from the supply duct improves you may want to discretely install a floor grille for additional return air. Is there a return on the first floor in the same stud bay as the above mentioned return?
 
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Old 05-25-20, 09:23 AM
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No, there isn't any return in any room attached to that duct run. That duct goes straight down to the basement from the joist bay. The only thing this duct run does is it picks up the return duct on the left side, in the basement.

In the basement I can see a piece of sheet metal blocking off the joist bay and that is right beside a duct created in the joist bay going on to the furnace return air ducting. I think I have another problem waiting for me there as I have no idea what they did to the joist in order to let the air get past it.

The way this whole thing is set up is either a huge error or the most sophisticated return air design known in the history of HVAC. I'm afraid to leave it as is and, at the same time, afraid to change it. I will try your tip and see what happens.
 
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Old 05-26-20, 06:53 AM
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The big questions which isn't covered in this thread is....
How has the heating and cooling been in this area of the house??
 
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Old 05-26-20, 07:14 AM
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That's the million dollar question tomf63!

We've owned the house, from the date it was built (1985) and it has been this way until I discovered it 35 years later. Really wouldn't be able to tell you one way or the other as I'm not sure how it should have been, if that makes sense. All I do know is that the room always ran a few degrees cooler in the heating season and a few degrees warmer in the cooling season. I just attributed that to being on the second story but it has been bothering me since we had the attic spray foamed and new insulation added a few years ago. The room does seem to be a lot dustier than the others upstairs.

I want to run the tip that 57Tinkerman proposed and see how that affects the room. I've not been able to get back to this project since they opened up the golf courses .
 
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