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Old 11-10-2015, 10:36 AM   #1
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Return air ducting


I'm finishing the basement in my 2012 home and just finished framing. All the supply runs were already installed by the builders, I just need to put in return air vents for two finished rooms, a hallway, and possibly for the unfinished storage area. I figure I need a return vent in each room the same size as the supply openings in that room, and planned on using the wall stud cavities to bring the vents down to floor level, but that's as much as I know.

Do I need to match the size of my return ducting in the study cavities to the size of the supply ducts, or can I just seal off the entire cavity and size the vent opening?

Do I just seal some sheet metal to both sides of the studs to create a duct within the cavity, or build a duct inside using duct board of some kind?

Do I need to widen my main return trunk line to allow for the additional airflow from the new return vents?

Thanks for any tips you guys can provide!
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Old 11-10-2015, 03:52 PM   #2
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Quote:
Originally Posted by MrAngles View Post
I'm finishing the basement in my 2012 home and just finished framing. All the supply runs were already installed by the builders, I just need to put in return air vents for two finished rooms, a hallway, and possibly for the unfinished storage area. I figure I need a return vent in each room the same size as the supply openings in that room, and planned on using the wall stud cavities to bring the vents down to floor level, but that's as much as I know.

Do I need to match the size of my return ducting in the study cavities to the size of the supply ducts, or can I just seal off the entire cavity and size the vent opening?

Same size at min, slightly larger is better.

Do I just seal some sheet metal to both sides of the studs to create a duct within the cavity, or build a duct inside using duct board of some kind?

Or run a bead of caulk on the studs, so the drywall seals the cavity.

Do I need to widen my main return trunk line to allow for the additional airflow from the new return vents?

Thanks for any tips you guys can provide!
You should increase your return trunk line duct, so it an better draw the return air.
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Old 11-10-2015, 09:43 PM   #3
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Thank you!

Using a bead of caulk makes sense. I assume that means using the whole 3.5" x 14.5" cavity isn't detrimental when connected to a 6 inch duct and appropriate grille for a 6 inch duct. Assuming I just caulk the drywall, is there a particular type of fitting that I should use to connect a 6 inch (or bigger) duct to the wall cavity?
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Old 11-11-2015, 04:13 AM   #4
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If your going with a drop ceiling, and have the height, a start collar. If your coming through the top plate, a basement boot. Althoguh a standard boot can be used, by caulking around it.

http://www.southwarkmetal.com/produc...egister-boots/
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Old 12-07-2015, 11:34 AM   #5
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Follow up question:

If I were to determine that I need to install a wall sconce in this particular stud cavity, is there a code-friendly way to install one that doesn't hurt the efficiency of the system? Maybe one of these with the wire ran horizontally through one of the studs and all openings caulked up?
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Old 12-07-2015, 12:57 PM   #6
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You can't run electrical through a return or supply duct anywhere that I know of.
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Old 12-07-2015, 02:41 PM   #7
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You can't run electrical through a return or supply duct anywhere that I know of.
I'm just talking about a stud cavity here, not a fabricated duct. I sure hope that's allowed, because the home was built in 2012 and the builders ran romex through floor joists in the basement which are also being used for return air.
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Old 12-07-2015, 05:12 PM   #8
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Romex/NM is allowed to run through a return. Its suppose to only be perpendicular, but parallel is often allowed to slide by the inspectors.
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Old 12-08-2015, 12:05 PM   #9
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Romex/NM is allowed to run through a return. Its suppose to only be perpendicular, but parallel is often allowed to slide by the inspectors.
Maybe it was just the pet peeve of the electrician I worked with occasionally back when I sold residential HVAC. He always wanted to meet with me before I designed my duct layout and he started pulling wire. He wouldn't pull any electrical (romex or otherwise) in stud cavities I was using as returns.
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Old 12-10-2015, 08:45 AM   #10
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Maybe it was just the pet peeve of the electrician I worked with occasionally back when I sold residential HVAC. He always wanted to meet with me before I designed my duct layout and he started pulling wire. He wouldn't pull any electrical (romex or otherwise) in stud cavities I was using as returns.
I definitely don't blame him, it wouldn't be my first choice.

I checked with the city inspector though and he confirmed that romex is allowed to be ran perpendicular to the studs/joists, and he said I could put a fixture in the cavity as long as I use a metal box and caulk it up really good.

I was hoping to use a 1/2" deep "pancake" box so as to minimize the disruption to the airflow, but it has to be installed in the middle of the stud cavity, so I need an old work box. The one I linked to earlier in the thread technically should work? but I'm not sure if that will support the weight of a wall sconce. As it stands now I'm thinking about installing a 8"x5" steel nail plate to the back of the drywall somehow (maybe fine thread drywall screws from the front?) and bolting the pancake box to that. It would be nice if they made plaster ears for round boxes...
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