Community: Mechanicals

I was told that my central AC needs a larger return duct. The symptom was that the low pressure line at the compressor was icing up on the outside. Does this make sense? I had thought that if the system was low on freon that this was a symptom.

I am handy but need some input into the size requirements of a return duct versus the output ducts. I would assume them to be about the same size.

Background: new home to be built in Zone 4A. Living area about 2200 sq.ft. on main level. On lower level is a 778 sq.ft. shop space, and 450 sq.ft. for future use. My energy rater estimates the cooling load at 18,000 BTUs for everything.

I’m thinking mini-splits. Mitsubishi offers several outdoor heat pump units that can have 2, 3, or even 4 zones, matched with any mix of the interior units (with an appropriate combined total of course). I’d like at least three zones to meet both distribution and the diverse needs of the spaces, but there’s a big question.

Plans / pics are attached

Exterior walls are SIPs R-24 with 1-1/2" EPS stucco
Center 'bumpout" is typical 6-9 stick with 3" EPS (interior to be sprayed)

WIndows are Integrity Low E3

window wall south facing

Proper way to heat and cool

We are in the process of building a very open floor plan home with catheral ceilings in CT (zone 5) with 2 levels.

Main level - 9-17' ceilling heights
Lower Level ( Walkout) has radiant in an exposed slab and footings over 2"EPS.

Does anyone have any experience with or thoughts on the hybrid "dual fuel" natural gas furnace systems that are combined with an air-sourced heat pump (instead of an AC only unit)?

The intent is for the heat pump to provide heat when its most efficient, but then switch to gas when the outside temperature drops to the point where the heat pump is no longer efficient or effective.