you only need about a 1"-1 1/4" under cut on the door to get a good return.30 square inches is good for 100-150cfm of return and this is plenty of return for any typical residential use of a room .if the square foot of the room is the size of a family room or large master bedrm then add a return And even if you cut a 6" hole for the pipe ,it is better than a 4"flex..If you have to lean into the door to get it to open from a 6" run ,this makes no sense ..are you growing something in this room???if so, you dont need to change the air that many times,use an ionizing air filter,and change the air ten times per hr...ha ha ha
..there is allways a way to get more air.you can remove the runs in the plenum and add a small main trunk up top,then add your runs to the main ,this will carry more preasure and less restriction ,and if you do that ,add a return trunk line ,and add a return in the ceiling ,this will make the a/c more effiecient
Originally Posted by Umby
I already cut out a larger hole in the plenum for the new 6" take-off, but the hole ended up being 7.25" which took up more room than I expected. I don't believe I can cut any more big holes like that one because I have little or no room now. I then put in a new supply register in the ceiling of the room in question (which gets little or no sun). Now when the air is on, I have to lean into the door to get it to open! I need to cut a c/a return on the bottom of the door. I would like to put at least one if not two more 6" supplies to other rooms, but now my plenum is getting full...