Matt, I didn't say it was ideal. In terms of design, there are a lot of fine points in the implementation and it's possible that with two different installations, in one home it works well and in another it doesn't, even if both homes feature the same floor plan and ceilings.

Just in case I misunderstood, the "typical" system I'm describing here has the furnace and AC coil ("the furnace") is in the basement and the AC evaporator somewhere outside. With basement ducts and 1st floor ducts in the basement ceiling. Then second floor ducts in the 1st floor ceiling. That means heat/cool come to the first and second floors via vents in each respective floor. This is what I understood that you were describing about your own system.

There's a lot more to efficiency and performance than just throwing a furnace and some duct work into a house.

Many, but not all, the homes in my current sub-division have employed a twist on this standard design. These are homes that were built in a factory and transported in one piece to the foundation. Theyre also designed to be Energy Star compliant. For the top floor, a central wide duct comes up from the basement all the way to the attic. Branch ducts then go to each room and vent in through the ceiling. All the ductwork in the attic is incased in 1.5 feet of expanded polyurethane spray foam (it's solid, you can walk on the stuff).

It's working reasonably well, though I am careful about which vents to leave open and which to close to move air around and create a stable/even temperature. The top floor doesn't vary from the first by more than 1-1.5 degrees. The exception is one room on the top floor that has a large bay window, in which the temps can rise significantly because of all the sun that enters. Plantation shutters takes care of that fairly well, along with keeping the fan on to move air around throughout the house.

Having some type of automated baffle system that could control airflow to individual parts of the house would be pretty cool, but I've never heard of such a thing being installed in a residence. That would be a neat way to direct airflow without requiring multiple furnaces or AC units.