I am in the middle of a remodel and the intake size is 12 x 20 and the house has a 2.5 ton. I am going up to a 3.0, 15 seer unit and one of the bidders tells me the 12 X 20 is fine and the other says it needs to be larger. I do understand that there are lots of calculations to consider in making this determination. Both contractors are about the same price. Thanks for any help.

are you saying u just have 1 return and its 12x20
you would probably gain by adding a second return rather than make the one you have bigger