I am in the process of finishing my basement and would like to add a cold air return. Fortunately, I have two ideal locations where the top plate of my stud walls run directly underneath a cold air return. In one case, the wall is made from steel studs and the other is wood. I plan on cutting through the top plate and into the cold air return duct and use the wall cavity as a duct. I'll install a grill to the wall about 10" off the finished floor.
Question: What type of hardware is available to accomodate this installation? Particularly, the drywall opening for the grill? Is there a mud ring of sorts that I can fasten to the stud wall so the drywall contractor can leave an opening? Also, should I line the cavity with anything?