2ND floor bedroom return not attached to main air return trunk

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Old 11-27-20, 12:54 PM
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2ND floor bedroom return not attached to main air return trunk

Hope everyone is safe and well. I have attached a drawing and a pic that I hope will help and the following background information.

I have a bedroom air return, on the second story, that is not connected to anything. All returns were installed using existing stud bays and then run through panned joists in the basement to the main return trunk.

It seems that they wanted it in that spot but when it gets down to the basement, there is a stairwell there so they couldn't get it across (no joist bay) to where the main trunk leading back to the furnace is located. To solve that (guess I should be glad they didn't just leave it) they went over one joist bay and ran a return up into the bedroom floor joists. Certainly had a fresh joist bay but the room has always been a bit muggy. Anyway, I blocked that one up and I need to attach the original air ducting to the joist bay going to the air return trunk. Problem is that the air flow is blocked by a double solid timber 2/8" joist. There is also a 5' flex duct in the way. I took a pic from the other side and i think something can be done there to get the original air duct connected to the duct leading into the main air return trunk. Thoughts? Thanks




 

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11-28-20, 05:19 PM
AllanJ
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Build a soffit about 16 inches wide and about 6 inches deep under the double joist to carry the return air from the dead ended joist bay to the next joist bay carrying the major return air flow. (Cut openings in the pans under the respective joist bays to connect to the soffit.)

Since the I beam is under the joists and detracting from basement headroom, the soffit can protrude down by a like amount without being obtrusive.
 
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Old 11-27-20, 02:30 PM
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Its pretty simple, air in = air out!
 
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Old 11-28-20, 11:41 AM
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Thanks for that math-splanation but how does it help me fix the issue I have?
 
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Old 11-28-20, 05:19 PM
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Build a soffit about 16 inches wide and about 6 inches deep under the double joist to carry the return air from the dead ended joist bay to the next joist bay carrying the major return air flow. (Cut openings in the pans under the respective joist bays to connect to the soffit.)

Since the I beam is under the joists and detracting from basement headroom, the soffit can protrude down by a like amount without being obtrusive.
 
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Old 11-28-20, 06:02 PM
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Thanks AllanJ. Would it be built out of sheet metal or does it matter (I mean most air returns in this house run in stud and joist bays)?
 
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Old 11-30-20, 11:34 AM
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Follow up question re soffit size

Sorry AlanJ. Just got a bit confused with the dimensions you gave. I feel like I need a third number to go along with the 16 and the 6 you gave. Do you mean something like in diagram (1) or diagram (2)? If, diagram (2) what would the depth of the soffit be (? in diagram (2))? Thanks


 
 

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