I am certainly a novice when it comes to HVAC systems and certainly don't know the proper terminology. I have a few basic questions about the location of the inside units, duct work, and returns. I live in central Texas and am building a 2 story 5200 square foot home with low E windows/doors and spray-in foam insulation throughout, including the attic. The units (3 3-ton units) I'm having are: Carrier Heat Pumps, 16.00+ SEER, high efficiency with 2-stage variable speed air handlers. All of the units will be in the attic but the location in the attic is my main question. In a well insulated home with the above units, what is the maximum distance a room being supplied by one of the units should be (maximum length of duct work) before you start losing significant efficiency (decreased air flow to the room with loss in coolness)? Basically, how important is it to have the main unit central to the rooms it's providing cool air to so the duct work is shorter versus the unit being farther away with longer duct work? I'm sure there are a lot of variables but maybe some general estimates or recommendations would help. Thanks