Forget what www.AceACandhackboyheatingco.com says . Get a load calc
done there is No rule of thumb unless you are a hackboy,
Gee Ace is the house in northern Minnisota with r 40 sips walls and
r80 sips ceilings with tri pane glass in the shade getting a lake
breese where a ton could be overkill, or in a desert in sun with r-1
in attic and no r in walls with single pane aluminum frames all facing
south where 3 ton is a possibility.
Gee Ace Hack I have high R , tri pane, dual pane, 1200 sq in the shade
and my 2 ton is to big , yes i need to run 2 dehumififiers and im
near Chgo. Yep im in the shade on a lake.