We also have a dual fuel HP in ATL (13 SEER + 80% NG furnace). If you're going to invest that kind of $$ in a new system, plus pay to operate it for the foreseeable future, I'd do everything I can to ensure I got a quality install. Below is a link to a Southface Energy Institute fact sheet on blower door and duct blaster tests. They're an ATL non-profit. I highly recommend the info they have on their site. They might even be able to help or point you in the direction of a contractor to design your system and/or test your house/ducts. Ideally, you'd have the blower door done to feed into the Manual J sizing of the system. Then, after your new ducts were installed and sealed (but before insulating), you'd have the latter done to test how tight the duct system is. A brand new system, installed right, ought to leak at about 0.05cfm/sq ft of living space. That's only 125 cfm for your house. If at all possible, you want to maximize the amount of rigid ductwork, only allowing flex duct at the runouts (I'd get at least the Vision Pro w/ an outdoor sensor to control the switch to Aux heat. My understanding is that the IAQ version will handle the staging possibilities better than the 8000 series VP. It also costs more. I'd also be interested in getting a HP w/ good low temperature performance. Our gas bills have gotten smaller since getting the VP set up to control the switch. But on an old house, you're still going to use gas for the days in the teens/twenties like we've seen this winter. Anyway, food for thought. We have used ACS to do work on our system. They sell Carrier equipment. Here is a link that might be useful: Southface on blower doors and duct blaster testing

Wow, the more I read the more confused I get. You all are great to help clarify. I've left a message for the Amana dealer to call me with a better explanation. With the AMH95, are there good vs. poor single-stage thermostats? It's all such a big investment I don't want buyers remorse - the Carrier system we've had might not be efficient, but for 35 years it's provided warm, low-maintenance, quiet heat! Life was simpler then i guess ... From http://www.nbnnews.com/NBN/issues/2007-01-08/Building+Products/30.html is the following sales pitch: "The Amana Two-Stage (Convertible) Multi-Speed Gas Furnace is available in both 95% and 80% AFUE and enables home builders to provide their customers with the quiet and comfort of a two-stage furnace at a price that is competitive with many single-stage models. Also, with a flick of the switch these furnaces provide two-stage performance  without the need for an expensive two-stage thermostat." "AmanaÂs new AMH95 95% AFURE and AMH8 80% gas furnaces feature the manufacturerÂs TwinComfort Two-Stage (Convertible) Technology, which eliminates the temperature swings resulting from abrupt, high-stage stops-and-starts of the furnace by operating at a low heating stage the majority of the time, for gentle, quiet heat. If the desired temperature is not reached within a reasonable amount of time using the low stage, the furnace automatically steps into the high stage."

You are not comparing like products. The AMH is a 2 stage furnace but cannot use a 2 stage stat. So it uses a variable timer from 1 to 16 minutes on low before it times to high. Most pros don't like that way of doing it. Eliminates the benefit of 2 stage being long run cycles on low in bitter weather. The AMH also has a standard blower motor. The AUH will stage based on needs of the house which is the way it should be. Also includes a variable speed blower motor for energy savings and some comfort features like slow speed constant fan and summer A/C dehumidify capability. How did they determine sizing? Is the old furnace 90% as well? 100K 95% seems like a lot of furnace for 2300 sq ft unless poorly insulated or a lot of leaky windows.

I have a few comments I'll make on all four systems, but the ultimate decision will be yours. First off, I am assuming all four contractors properly sized your house's heating/cooling system based on a load calculation, or at least isn't oversizing anything. It is good to see that the sizing is in the same range across the board, with the hope it is correct. 1. Very nice equipment. Probably want to get the model number on the a/c unit as well to have it in writing. Ruud has high and low end equipment models, just like any other brand. 2. Nice system, comparable to the Ruud with the 2-stage advantage on the a/c side of things. PROBLEM: That's not the thermostat you want. That particular model only controls one stage of heat as far as I know, and you want one that can control both stages of the furnace's heat. Don't let them configure that nice furnace to just run off a timer. The Honeywell 8000 quoted in the others is a much better option. 3. The Infinity system, as I'm sure you've read, has its bonuses as far as indoor comfort control goes. However, the price justification is up to you. You can and will achieve similar results with either other system set up properly. If they use the old lineset, fine, but they should flush it out well. The 24ANA748 does not have the scroll compressor, which I personally prefer. It has the reciprocating compressor which stops in between stage changes. 4. No additional comments other than making sure the lineset is flushed out before reuse. Also, the HC-10 is a Lennox part number, not that it makes a huge difference for the air cleaner.