[Evans, Marv]

I'm not an HVAC guy either, so can't offer any specific suggestions. Our place is smaller than yours - 3200 s.f. It has 10 ft. ceilings throughout. One thing I figured out, especially during winter, was that the air could become stratified with the warmer air rising & leaving the cooler air below. That is with two, 20 in. square returns. So I felt the air needed to be circulated more. I bought two fans, one for the living room area (it's pretty open with the entry, dining area, kitchen & "sunset room") & one for the master bedroom. They are quiet (went through a couple of fans to find sufficiently quiet ones) & adjustable in terms of vertical and horizontal circulation patterns. They reduced the amount of time my heating system cycles on & off & mix the air. Maybe you could benefit from that kind of thing. If I knew what I know now, I would have installed a couple high in the walls in strategic locations with grates during construction.