Your existing system is either a 10 or 12-SEER unit; they were good performing units, & a new one, especially if oversized may not produce any savings over the older unit. A 3-Ton properly installed & setup unit should cool your 1700-sf home at your location. You can always do cost effective things to reduce the heat-gain. It is all in how well everything is design-engineered... In fact a 2.5-Ton unit might cool it; that is only 600-sf per/ton of cooling. I cool my farm home with a mere half-ton window unit for the entire 1st floor; that's around 1200-sf per/ton of cooling in very hot & humid weather extremes. Slightly less than a half-ton upstairs -.cooling 2 bedrooms a bath room & hallway; usually only run it for a while before going to bed unless a real hot day & night. A 5th grader can perform that LINKED load-calc print the instructions & follow them! Here is a link that might be useful: Free Whole house Load-Calc

Tigerdunes brought up demand defrost versus timed defrost. For the past 18 years, I have dealt with my Lennox defrost scheme. The only times I heard it go into defrost mode were when the unit was first running in heat mode. The unit would switch over from heat to defrost, the defrost cycle would complete and everything would turn off. I never heard it run a defrost cycle when it was not first heating. I rarely heard it go into defrost. I never heard it defrost on a fixed cycle such as every 90 minutes. Am I to understand that a Carrier will just go into defrost mode every X minutes whether it needs it or not and is not in a heating cycle; just turn on and defrost itself? I found this information in the Carrier 25HNB6 heat pump installation instructions: AUTO defrost adjusts the defrost interval time based on the last defrost time as follows: When defrost time When defrost time 3-5 minutes, the next defrost interval=90 minutes. When defrost time 5-7 minutes, the next defrost interval=60 minutes. When defrost time >7 minutes, the next defrost interval=30 minutes. The control board accumulates compressor run time. As the accumulated run time approaches the selected defrost interval time, the control board monitors the coil temperature sensor for a defrost demand. If a defrost demand exists, a defrost cycle will be initiated at the end of the selected time interval. A defrost demand exists when the coil temperature is at or below 32_F (0_C) for 4 minutes during the interval. From that description, if the time interval elapses and the coil is not at 32 degress, then no defrost will take place. That, to me, sounds like a form of demand defrost. Is Baldloonie saying that the coil could be at 32 degrees or less without frost and, therefore, a defrost cycle would be unnecessary? What kind of ambient sensor detects presence or absence of frost? Neohioheatpump asked, "When your old A/C would run, was it producing water?" It was producing water and I saw it dripping from the condensate drain. One weekend I went out of town and came back to find water on the floor around the return box that the fan coil sits on. I opened up the access and found the interior insulation of that box soaked. Turns out the condensate line was plugged. Took awhile for that to dry out. On the other hand, this past summer I did not see water dripping from the condensate drain. The drain line was not plugged and the drip pan seemed dry. I thought it was because I had dried out the air so much with the two dehumidifiers that there wasn't enough remaining for the A/C to remove. Cooling was normal. Running the fan on manual started with the installation of the Lennox and an associated Honeywell Electronic Air Cleaner. The house suddenly became dusty and I blamed the EAC for not doing its job. The Honeywell zone representative came to my house, sized up the situation, and told me to run the fan on manual so that the dust would remain suspended in the air and available to be captured by the EAC. I did that and it was of no help for the dust situation but it did help reduce the temperature differential between the first and second floors during cooling so I kept doing it as a matter of routine. Thus, I cannot say that not running the fan reduced the humidity. Though I complained about humidity, the heat pump contractor never told me that I was humidifying the house by running the fan (on orders from the Honeywell rep). I will continue to run at least one dehumidifier in the completely below grade basement during the summer because I want that area to be warm and dry to avoid mold and mildew. I've been in the basements of other houses in the area that don't use dehumidifiers and they stink. Mike Home said, "You stated in an earlier post that you run the fan in the summer because the upper floor is 2-3 degrees hotter than the lower floor. I think adding the attic insulation will help this." I agree that adding attic insulation could help. But, having a Dutch Colonial house with a barn-like roof that is covered in dark shingles on the east and west sides causes a lot of heat gain through the second floor walls. I'm not keen on opening the walls to determine the amount of insulation or add to it. Changing to a light-colored roof would make the house look out of character with the neighborhood. There are newer shingles that reject heat gain that I will investigate. Mike Home also said, "You could also zone the first and second floors, but this is expensive and probably not feasible with your current duct work." There is but one main feed duct and it runs through the basement. There is no way to segregate the room feeds in this scheme without doing each one individually. I'll leave that expense to the next owner.

The winter design temperature for eastern Nebraska is about -3 degree F. In my opinion you are making a mistake by not getting a 95%+ efficiency furnace. If budget is an issue then look at the other Trane furnaces. The variable speed motor adds a significant cost, but I personally think it is worth the investment. You current furnace must be very loud when it is putting out 150K BTU. A new variable will be so quiet in comparison you won't realize it is running. I doubt you need a 5 ton AC condenser. Keep looking for a contractor who will do a load calculation. The XB16 is a single stage compressor. I don't see how it could have the same compressor as the the 2-stage XR17. That makes no sense to me. I would think a 4 ton condenser with a 80K or 100K furnace would do fine with your house and climate. But rather then guess, get a calculation and start saving money.

Has any contractor done a load calculation? It is difficult to tell from your posts whether the sizes are correct. 160,000 BTUs for heating, and 4 tons for cooling seem big, but they could be correct. Did you ever get accurate area dimensions for the first and second floors? Why the XV80 and not a XV95 for the second floor? Is it a cost issue?