Now that I have fininshed sealing my ducts and returns my static pressure has rissen to .88 @ 1600 CFM. So my next project was to increase my return grills. But then I got to thinking. While I was sealing the return ducts, the builder only punched small openings through the floor. I didn't measure it at the time but I guess they were around 2"x4" or 3"x6" something in that general size. The returns are using the house beams and not seperate pipe.

So if I where to increase my return register size, I'd still be resticted in the walls due to these openings, woundn't I?

What size is normally put into the floors/cellings for returns?