"Most everything, HVAC wise, in my home is working fine. But, I would like to correct some things that were done before I moved in. I have 2 rooms that are supplied w/ 1 large duct. The end of the large duct run supplies 1 room & a rectangular hole cut 8' away, serves as supply for the other room! There is no return for either room! (or in this part of the house) I want to correct these supply & return issues. Bedroom 1 is 11'2" x 16'8" and is approx. 24' from the main unit. What would be the proper size of the supply duct? Bedroom 2 is 14' x 15'3" and is approx. 17' from the main unit. What would be the proper size of the supply duct? Now the returns. Would 8" flex for the returns in bedroom 1 & 2, be OK ??? ( I have access to free 8" flex duct !!!) Also what would be the proper size of the return grill, with a filter, for these 8" returns? All of my returns have the filters in the living area, so I do not have to go into the attic. Thank you in advance, Paul in Texas."