I have a another question if some can field it.

The number of air returns, what would be best way to determine if i need more. I been read on internet about this problems with not have enough returns.

We have a huge 25 X 20 x 22 h room with cathedral ceilings with one small 10 x 8 return that is jumped to another return threw the wall up into a bed room.

Also can i add another return air vent , to an existing return run without loss air flow? Would i gain more air

flow or just divide the air in two ( between the two vents).

I think it would work well if starved for air.