Jt Some questions please. What is your location? What size home living area? What size furnace and eff are you replacing? What size AC are you replacing? I would like to know the exact mdl number evap coil for each quote. What thermostat is proposed for the Carrier quote? That is a big difference between the 96% eff Carrier furnace and the 80% eff Trane furnace-both 60 K input. That would be about 56 KBTUs output on the Carrier and about 48 KBTUs on the Trane. Not insignificant. I don't care for some shortcuts that homeowners make particularly on reusing linesets and using existing thermostats that shortchange a nice furnace's operational capability. Post back with the info requested. IMO

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.

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?

WHAT IS A HIGH LIMIT SWITCH? https://www.newcentralairconditioner.com/ The high limit switch in your gas furnace is a small part with two very important jobs. This switch plays a role in the normal operation of your furnace. Turning the fan motor on and off is the high limit switch’s main job. This is the role it plays in every cycle of your furnace’s normal operation. But that’s not the only thing that the high limit switch does. It’s also safety device that helps prevent your furnace from overheating. The high limit switch consists of a long temperature-sensing probe attached to a metal mounting plate. From the mounting plate, the switch is wired to the blower fan motor and to the gas valve. The switch is generally located just past the heat exchanger. This is so that it can detect the temperature of the supply air. In other words, the air that’s about to be blown into your home.