This could be the most intelligent comment I ever read a HO make. Then maybe your an engineer. Either way I wish every customer thought like you.
Originally posted by engineerguy
My own super insulated, super tight 1320 SF home has a calculated cooling load of less than 9000 BTUH and heating load less than 19,000 BTUH. The air handler runs at 400 CFM for both heating and cooling. The one ton AC is definitely larger than necessary for 90 plus degrees outside and 77 degrees inside. With five registers, one for each bedroom, and two in the kitchen/living room, we have plenty of air circulation.
Do not oversize the AC. If it's slightly too small, the house temp will rise a degree or so in the late afternoon. A ceiling fan is nice for the living room in summer.
You will almost certainly need a whole house dehumidifier.