We are building a new home with approximately 5500 conditioned square feet on 2 stories and are looking at different HVAC options including conventional heat pump(s) w/ or w/o outdoor furnace or geothermal heat pump(s). We have received estimates from 4 contractors. Three of the contractors recommend 2 units - one up one down, with sizes varying from 5 tons for both to one 5 ton down and 31/2 ton up. The fourth contractor recommends a single 5 ton, dual stage, variable speed unit (the other contractors did not mention the dual stage or variable speed). The fourth contractor is the only one that did any homework before making his recommendations. He sized out the house (we are done with framing) and performed a load calculation/right J.

I am definitely not an expert (wouldn't even consider myself a novice) on these things. My question: Is it possible to condition this much space with a single unit?

I am not sure what info one might need to respond to my question, but will try to provide any additional info needed.

Thanks!