RO For Return

GenConJ

I know almost nothing about heat pumps. Need to frame out the return vent.
Does the opening for a return vary depending on tonnage of unit (3-5 tons)?
I am guessing an opening at 36 x 24 x 19 deep. Too much? Not enough?
For me the smaller the better.
I am figuring a 4-ton 12 seer unit in this house.

HVAC Doc

For a 4 ton unit, you are going to want to be able to move right at 1600 CFM of air. The absolute smallest you want to make the opening is 20x20. Smaller isn't better when it comes to pulling return. Better to have "too much" than not enough. Most manufactures specify the use of at least a 16x25 filter if not a 20x25 in the return stream.

GenConJ

Thx Doc