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

"One of the worst things that you could do in a house is install leaky ductwork in a vented attic." - Joe Lstiburek Vented crawlspaces can be even worse with humidity and soil gas issues. Worst case: In the OP's case which is "unfortunately typical" you get this: With that improvement, according to Lstiburek, you can still expect 30% higher heating and cooling costs compared to best example: Notice insulation at attic floor, not roofline. Taken from Joe's BSC resource: Are you doing something stupid? Many designs call for insulation at roofline, just make sure it meets minimum code prescriptions. The biggest problem with roofline sprayfoam is the allowance of ridiculously lower than code R-value minimums. The home as a system is big and complex. It's easy to break out any one component and argue that it's not a big deal to compromise on efficiency. The more one applies that philosophy, the more performance will suffer. It's not just energy use, indoor air quality and uncontrolled moisture movement are also influenced by these decisions. Not accusing anyone but HVAC contractors are notorious for selling oversize systems that increase profits with bigger equipment markups. I can also imagine contractors used to installing attic ductwork might frown on the better practice of conditioned space ductwork as it may create more headaches coordinating with construction teams not used to doing it. Slabs, increased window area and typical construction are not good excuses to continue poor building practices. I'm all for balance but significant ductwork in vented attics or crawlspaces is tough to justify for new construction.

The condensate collects inside the air handler where the evaporator coils are, you should have seen the pan and any tubing. There must be a pump that takes the water outside? The only connection between the outdoor coils and the indoor air handler are the refrigerant lines, and they are sealed, with liquid/gas refrigerant inside. Nothing for you to smell there unless there is a leak, and then your AC would not be working. I’m guessing as to the configuration of your system, outside condensing unit (heat pump?) and indoor air handler with duct work that goes to various rooms. Using my imagination, I have no idea what you actually have there. How did the AC guy clean the coils? Did he use some kind of chemical that you might be smelling? Maybe close to the garage wall? Hosed it off? If he used a chemical, can you ask to smell it? Does the upstairs system that you don’t use have it’s own condensing unit and air handler? I’m not an expert on this, I just used to work for an HVAC company many years ago, not as a technician though. Maybe someone with another idea will chime in.

The biggest problem with HVAC zone systems is knowing when to choose it as a solution and when not to. Some HVAC companies it's about "sell, sell, sell" whether or not it works... there's more money in "sell, sell, sell" --- when it's only about money? So does the comment above mean I do it for free? No. If you think that you are reading things that aren't there. New construction? best to choose separate systems 9 times out of 10. In order for a zone system to work, you have to know what you are doing. Most HVAC companies staff (the techs they send you) are 20-30 year olds. How much practical experience could they possible have? It's best for HVAC zone systems to be an elegant solution. A HVAC zone system is a tool in the tool bag. Not all homes are suitable for zone systems. Some homes there is no other way, and in some cases complications to those problems will make an HVAC zone system design possibly more prone to problems. You have a problem now, do you want more problems. These decisions among others are decided "in person" --- so considering that becareful what information you decide upon from the internet. Just because it's here doesn't necessarily mean it's true. That said: Depending on equipment level chosen, how many different floors you have in your structure, how much room you have available... will all be factors that make you decide one way or another. From there it's in your best interest to pick a contractor that is skilled: especially when it comes to HVAC zone systems. (there's a lot of garbage out there.) (click to enlarge if necessary) I service the Katy, Texas area.