Doug,

You are on the right track. You can't blow air into a coke bottle.

The return air duct your talking about doesn't have to be over the door. But
further away from the supply duct to the room is a good idea.

Commercial sites use 'cross-talk silencers' I think is the phrase. A duct that
goes up, over to the next room and then back down into the ceiling again. Any
decorative grill would work that allows the air to flow through freely. Remember
that a fan is pushing the air into the rooms and that same fan must suck it out.
So make it bigger than the supply duct. For sound isolation, the metal duct is
coated internally with this black fibreglass insulation. It keeps the sound down
a lot between the spaces.

You can make them up yourself or get a sheet metal shop to make them for you.
They do the insulation very neatly as well. Shape them to suit your construction
needs. As long as the over all shape is a big letter C, then it should work fine.

Dave


In article .com,
wrote:

I live in S. Florida and want install transfer grills above the doors
of our bedrooms to increase the return air flow back to the main return
grill in the livingroom. Currently the doors are slightly cut on the
bottom but I don't believe it provides the proper amount of return air.

Snip"