75K high-efficiency upflow unit. No A/C. 16.5x20" opening. I need ~300 sq. in worth of supply.
Square ducts, so it can come mostly off the top if the sides angle outward into a 22x20 top. Maybe one 3.5x10 in the side.
I'm thinking 20" high for the box, plus head space for two 7x20 elbows. Can it go shorter? Does it need to go taller?