I have several bedrooms that have less-than-desirable return air flow at night because when the bedroom doors are closed, air can't get to the central return ducts (which are in hallways). The bedrooms have air vents in the ceilings, and I've been told that the best place for return ducts is therefore near the floor.
However, it's not very easy to get the ducts near the floor without tearing out walls, which I'm reluctant to do.
I read somewhere else that one potential work-around for this is to use the space between the studs in an interior wall for return venting, and then to just connect a flex duct at the top stud that runs back to the main return vent (I have pretty easy access to all the bedroom ceilings). In other words, the air enters the wall through a grille near the floor, travels between the studs and up through holes drilled into the top header, and then goes into a regular duct.
Anyone ever done this? Any drawbacks to this approach?