Interesting, but frustrating problem.....
Have a 1300 sq. ft. single story ranch in Florida. Master bedroom(front of house) is facing south/southwest, so it always gets full sun in afternoon and evening.
Bedroom door opens into living room area. Bedroom has 10' vaulted ceiling. Living room has approx. 14' vaulted ceiling. The only air return is just outside and above the bedroom door.
The problem is the master bedroom is always 8 - 10 degrees warmer than any other part of the house. The entire ceiling throughout the house is insulated very well.(crawled up and checked.) The small "master" bath is a few degrees cooler even though it has a skylight and I've left the register closed.??? Doesn't make sense to me there, but.... whatever.
The garage is next to the bedroom and bathroom and the garage ceiling is uninsulated. The air flow above the garage is able to flow into the rest of the attic space.(There is no wall in the attic to prevent the hot garage air from spreading to the rest of the attic, but again the ceiling of the entire living quarters is well insulated.
I have closed all the registers (to experiment) except the one in the master, but it doesn't seem to make a huge difference. The master register does blow cold air well.
I've even placed cardboard(I'm sure the neighbors just love it!) in the master bedroom window. It helps quite a bit, but still nowhere near the rest of the house temp.
One problem I know is that my windows are crap. I can fix that later. Cardboard will be a temporary fix. heh
I have ventilated soffets on the eaves of the house and only one small gable vent on each side of the house.
I'm guessing that if I put in at least one attic fan on the southern facing roof near the ridge line it can only help, but.....
Would adding a pass through register above the bedroom door help to equalize/improve air flow from the bedroom. Again I have vaulted ceiling in the bedroom, so I'm assuming a lot of that hot air won't sink(because hot air doesn't) to go through the door(which is usually left closed)???
Any other suggestions??????