The return air on my Rheem Mod is attached on the left side through an Aprilaire 2200 media filter that is mounted directly against the side of the furnace. The MAX cutout on the furnace can only be 23x15. The Aprilaire outflow opening is about 22x20 inches, so considerably taller but also narrower than the furnace cutout.
So the max furnace cutout is 345 sq.in., the max filter cutout 433sq.in., but when you matchup the two the opening shrinks down to only about 330 sq.in.
A lot of the filter is just up against the side of the furnace, not into the return air cutout.
I'm sure this is very common in a lot of installs since none of the Aprilaire units seem to match the max furnace cutout.
Doesn't this create extra resistance in the return airflow to be concerned about?
Whould this have been a better instalation if the furnace had been set up even 8 inches on a sheetmetal box and the return run into both the side and bottom of the furnace? Or am I just being anal and its fine the way it is.