I have a 4 ton American Standard electric forced air furnace (with no A/C - just heat) with a single speed blower motor, circa 2006.
My supply main trunk is 12"x20".
The return side of the system has not yet been completed. Is there a standard rule of thumb for sizing the return side of the duct system?
EDIT: Ok, clearly this is a more difficult question and answer than I anticipated. Does anyone have a general rule of thumb for the ratio of a single trunk supply to a single trunk return? i.e. In any given installation should the return/supply ratio be 1:1? Should it never be less than x:1? Any input would be appreciated.