I have a 3,200 sq. ft. single level home servced by 2 - 3 ton AC unts. The duct work and air handlers are in the attic. The first until services the LR/DR/Kitchen/Den, all fairly open areas. The stale air return is a 20" x 20" opening in the ceiling.
The second unit services 3 bedrooms. Two of the bedrooms, each about 250 sq. ft. (9' ceilings) have 2 - 4" x 10" supply vents each. The master bedroom is 15' x 20', with a 7' x 15' dressing room (9' high ceilings). This room has 2 supply vents in the ceiling and one in the dressing room. The stale air return for this AC unit (20" x 20") is located in the main hallway. There are no returns in the bedrooms.
Normally we keep the bedroom doors open, but when we close them, the airflow into the room is reduced. The airflow is quite strong and if we leave the doors open less than 4" open, the airflow will suck them closed.
We are not interested in making large undercuts in the doors as this adds noise from the hallway (and ruins the carpet with dirt). I believe the air handlers are moving 1,200 cfm each.
Question: What size returns would I need in each of the 3 bedrooms? Is there a way to make sure the returns don't add air movement noise from the air handlers in the bedrooms?