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

I would recommend a heat pump in your area, because for those 2 months or so you do use heat, it's much cheaper heat than electric heat strips. Also the requirements to get the $1500 tax credit are lower. Looks like you're looking at 3 ton units, which I'll assume is correct but you want to have a load calc done to determine this (and have your ductwork checked to determine proper size, etc.), so here are a few ideas for Lennox setups since you're interested: XP14-036-230 heat pump CBX32MV-048-230 air handler Honeywell VisionPRO IAQ thermostat (best for dehumidification by controlling blower speed) backup heat strips (customary to install on any heat pump install but needs to be in the estimate) = 15 SEER XP19-036-230 heat pump (2-stage - helps with dehumidification) CBX32MV-048-230 air handler Honeywell VisionPRO IAQ thermostat/Lennox ComfortSense 7000 thermostat backup heat strips = 18.6 SEER The Signature Line of equipment will run higher in price, probably around your York YZH price tag. Both qualify for the tax credit, so - $1500 along with any other rebates you may receive. I would recommend either of the two setups to you above, as well as the Trane XL15i heat pump (single stage) also qualifying for the $1500 tax credit: 4TWX5036A1000AA heat pump 4TEE3F39A1000AA air handler Honeywell VisionPRO IAQ thermostat backup heat strips = 15 SEER If I were looking into replacing the system at my house, Trane and Lennox are certainly two of the brands I'd consider.

a heatpump is just an a/c with some extra controls and parts. It pulls the hot air out of the cold air outside and and puts the warm air into your home. It works especially good when above 30 degree's outside. Basically the air conditioning cycle reverses. In the hot 95 degree outside air, your air conditioning makes cold air. If you put your hand on top of the outside unit, you would discover very hot air coming off the top. If you put your hand on top of the heatpump when running in cold weather, the air off the top would be extra cold. It would be moving the warm air into your house. This method costs about 1/3 even 1/4 the cost of electrip strip heat. Instead of generating heat, its just condensing and moving heat from outdoors to indoors.

York YM9M isn't variable speed. Request a Honeywell VisionPRO IAQ (preferably, if not the VisionPRO 8000 will be fine) as it can slow the blowers down to dehumidify on demand and is an overall nice thermostat. The Affinity is a nice line of units, so you may want to look at the YCB 13 SEER Affinity line. Not a big fan of 2-stage A/C. I think single stage properly sized is more than sufficient with dehumidification controls (the IAQ). It's never a bad idea to get 2-3 bids for a job like this. Did they size the equipment per a load calculation (called Manual J)? Did they make sure your ductwork was adequate? More goes into this than just the equipment.