I have a 3ton HEIL outside unit made in 1994 - model number npahc36ak01. I can't figure out what size duct work to use on the return and intake? anyone have any ideas on what size I should use on these? The return and intake are different sizes. The return I believe is 14inches and the intake (which is an odd shape) is 11inches in height, can't remember the width.
I would hook up whatever fits. Is it square or round? Our sheetmetal shop made the transitions, we just installed whatever the salesman said. They made us square to square, square to round, and made the shroud to go between the package and house.