I have at least a one inch gap under my bedroom door. I was planning on cutting in a cold air return in the wall but was wondering if the gap is letting enough air back through already. The furnace has a central cold air return in the basement hallway and the plan was to put in a "pass through" vent in the bedroom wall. It's been functioning alright w/o it so far but I don't know if I should still cut a hole in my wall if I've got this huge gap under the door.
The gap under the door will serve you fine. In fact that's one of the reasons it's like that.
The problem with a passthru vent is that it will allow sound to pass right thru too, which is usually not a good thing.
I would be inclined to suggest, if it ain't broke, don't fix it.
PS Oh yeah, the whole reason I clicked on your thread, was to point out that "Cold Air Return" is a bit of a misnomer and a personal pet peeve of mine. It's much more accurate to leave off the "cold air" bit and just call it return.