What material do I need to place on both side of the wall to return air before I put drywall on top of it?
The return register will be install close to floor level and the wall is made of 2×4 lumber.
Thanks!
HVAC – Does a Return Air Cavity in a Wall Need to Be Lined?
hvac
Related Solutions
Non PT wood will be fine.
I would build a 32x22" frame out of 2x4's but I would put a 3/4" square notch around the inside diameter of the frame and set the filter into that notch. That will give you a nice seal for the filter but prevent it from falling through. If necessary, add one or two cross braces across the inside of the frame cut to the depth of the notch so the filter has extra support.
This is an acceptable solution for multi-tenant buildings where the exhaust fans from multiple units vent in to a common duct. The booster fan in the floor vent makes sure that the air pressure in the room being vented is higher than the common duct. The booster fan can pull air through the central AC/hear air handler even if it's not running. This lightens the load on the exhaust fan.
Related Topic
- Should I install a damper above the return air duct for better upstairs cooling
- 180ยบ/gooseneck/u-shaped cold air return
- Ramifications of adding a second HVAC air return (in parallel)
- Return Air location
- Electrical outlet above HVAC air return, within same wall cavity
- Wall Register – How to Easily Split a Wall Register
Best Answer
In terms of sealing a return vent, it is sufficient that the drywall and studs are compressed to create a channel in the wall. No need to caulk the corners, unless there are gaps. No metal lining needed.
For wall to floor transitions you can cut sheet metal to create a custom fitting (box), and seal its metal seams with tape or mastic duct sealant. Lip the metal over the drywall and screw it through the drywall into the stud. The grill will cover this. Screw the other end of the box to the return duct.
Most return in-takes I have seen have no additional sealing. There is a grill in the drywall, a cut-out in the bottom plate, and a blocking horizontal stud behind the drywall above the opening. Sometimes there is a metal return air box, but no additional sealant.
In stead of lining a drywall channel (because it has gaps and cracks), you can use round ducts and squeeze it into an oval or ellipse to fit in the wall cavity (e.g. a 8" duct in 2x4 framing). Since this is more restricting than a rectangular duct/channel formed by the drywall and studs, you'll have to calculate the area of the oval's cross section to make sure is sufficient for the required air flow.
Image from http://www.ductworkinstallation.com