The DOE has worksheets that can help you calculate the relative cost of heating and cooling with different systems using your current energy costs. Of course you need to predict the relative costs over the next decade or two to really tell what is best. How is your crystal ball working? I would like to clear up a couple of common misconceptions. One type of heat does not dry a house in the winter any more than another. Leaky house envelopes dry houses. Heat by flame of some sort might dry a house more because they draw more outside air in if there is not a source of outside combustion air. That would be the only mechanism. There is nothing special about heat pumps in poorly-insulated, leaky homes. No heat or air conditioning source works as well in that situation as well as they do in tighter, well-insulated homes.

First - Trane (Bryant) has the best rep in the coastal areas. I recently built in a coastal area and put 2 trane heat pumps in for 2 floors. I also built a larger house with less tonnage than all your quotes. And I had less insulation. Windows and orientation are what matters but 5.5 tons for 2100 sqft is very high - especially for new construction. The number one problem with HVAC quotes is oversizing... I'd probably go with 2 units but there are other details that matter more. As far as furnace, you don't mention what you have available. I suspect that NG is pretty rare in Fl and that is the only fuel where a furnace would make sense. If you don't have NG, you would be a fool to put in a furnace.

Hybrid heat is the way to go! Look for a system the qualifies the heat pump for the tax credit on the tax credited heat pump It takes a HSPF of 8.5 or greater. Rough estimated COP from 8.5 HSPF is High temp COP 3.7 Low Temp COP is 2.7

where does one find "degree days Centigrade scale" for their climate? I am in Sarnia, Ontario and this is an area where a heat pump supposedly feasible. (i would mate it with a high efficiency furnace), but all the techs i speak to have advised against it saying i am wasting my money, it won't work...etc. I have gotten a couple of quotes for 16 seer 2 stage heat pumps with HE furnace and they have been 11-12K. i can get the same setup with 16 seer ac for about 8K... doesn't that seem like a huge jump for a heat pump over an a/c condensor? i'm about to give in and just go with an a/c unit, but the math says it is about 30% cheaper to heat my house with at heat pump over a 95% efficency furnace...and that is using a COP of 2.5 at 30 deg f. i am thinking about importing my own equipment from the states where prices seem much more reasonable (96% amana furnace 16 seer 2 stage heatpump, coil, txv for $3800) and just having a local guy who is willing to install it. that blows some of the rebates that are available, but it still might be worth it. all i know is it would take more than a decade (and likely much more...) to recoup an extra $4k.