I've got a suburban nt-34 furnace. As built it has 2x 4" ducts openings on either side and a rectangular duct opening on the bottom.
According to the manual it needs 48 square inches of duct to food out to.
On the original setup there were 2x 4" outlets used on one side and the bottom duct fed out through a duct that sat right on the floor. Totaled. 48sqin.
New face frame kitchen cabinet makes using the bottom duct not the best option.
Can anybody think of a reason why I couldn't cut a hole in the front access panel to make a duct run through there? If you take the panel off you're staring right at the other duct outlets so it's essentially the exact same place as the other ducts come from.
I'd probably cut a 6x4 hole and put a baffle plate set bank 1" inside the panel so all the air doesn't shoot straight out hogging from the other ducts.