My other contractor offered putting 5 ton coil on 4 ton ac unit. Does it work or is it a sales gimmick. Also what size filter would I need for 4 ton unit.
With your load conditions I would stay with a 4-Ton indoor coil, the compressor will be able to pull the pressure & temp down a little better at particular loads which will be helpful for humidity control.
IMO, the slight gain in SEER is with lab conditions &, would usually be immaterial in your conditions in Detroit.
Thank you for your advice. Is there a way to calculate by how much the heat load will be reduced if attic insulation goes from R-35 to R-60 for example. Also, should the contractors perfom manual D calculation or is it only done for new construction or remodeling