Is there something wrong with the A/C? Usually 10 years is a little young to be replacing a good system. But, yes, dual fuel in Hotlanta is a good move.

Based on the information you've provided, sounds like the York quote is the best option, but I don't agree with the 80% modulating furnace. That's a high-end furnace, and going with the 80% version doesn't make sense to me, especially in our region where it can get cold at times (I'm in Maryland). Is PVC venting an issue? The York Affinity is a nice line of equipment. American Standard isn't bad, either, but the equipment that the York rep. is quoting is better in my opinion. 3 tons is a bit much for your cooling load, but it's what you'd have to go with if you went with the Affinity line. The 2.5-ton Latitude unit would be the better fit. With the low stage on the Affinity approximately meeting the cooling load at design conditions (which won't be met on all days), I don't think you'll be getting those long run times that you should with a 2-stage system. Ask the York rep. if he can quote the CZB or YZB 2.5-ton single-stage Affinity unit with a 90+ efficient v/s furnace (modulating or 2-stage). Not sure where the American Standard rep. came up with his sizing. Do you like it cold in your house (68-70)? Did the York rep. do the load calculation?

vstech, I read the install guide for the dual fuel kit (Dual fuel kit Trane TAYPLUS103A) they sent and it does mention a Bonnet Thermostat but in the notes it says this is only required for oil furnaces. I'm getting a gas furnace. It also looks like I'm loosing my 2-stage gas furnace with this dual fuel kit because it says to jump W1 & W2 on the furnace. I'm still not seeing how this thing is going to help my system???

Thank you all for your replies. I did download the installation manual, and after mapping out all the wiring, I found out why the pump was always defrosting and corrected it, along with some other wiring mistakes, and I replaced his wires twisted around the relay terminals with proper spade connectors. I also found a dip switch on the thermostat that was causing the 2 minute delay. However, I couldn't find an exterior thermostat as ziggyhere mentioned, but the heat pump's wiring diagram shows a temperature sensor; could the old system have used that as the outdoor thermostat? If not, my parents are on a dual rate from their power company: they get a discounted rate as long as the outside temp stays above -12 degrees Celsius or around 10 degrees Fahrenheit. The power company installs a temp sensor in a housing that mounts between the meter pan and the meter itself, with 24 VAC present at the furnace when the temperature is above the setpoint of 10 degrees. Could the old system have been using the signal from the POCO sensor to shut off the heat pump and switch to oil? Also, when the temperature outside was around 16 degrees Fahrenheit, sometimes the oil burner would come on for a couple minutes (and the heat pump would shut off), and it doesn't do that anymore; could that be a feature of the old system, or could it be a feature of the heat pump itself? Also, with the old system if we raised the thermostat's setpoint even by a few degrees, the oil burner would kick in until the desired temperature is reached, but the new system doesn't do that; is it typical of dual heat systems, or was it just a feature of the old system and I shouldn't worry too much about it? Finally, I have heard and read several times that below a certain temperature, heat pumps lose their efficiency and there was indeed a chart in the heat pump cover, but after 21 years out there, it isn't legible anymore. It's an ICP 2-ton unit, if that matters. Because the system would often rely on the oil burner past the 16 degree mark, I assume that is where that particular heat pump starts losing its efficiency. Is it putting more strain on the compressor to let it run below that threshold? Thanks again for taking time to help me, and have a nice day!