Costco is working with a fairly reputable contractor (according to Angie's list anyway). Second estimate direct Carrier authorized contractor (distinguished/presidents award according to carrier's website, for what that is worth). Price was almost $3000 less than Costco for similar A/C systems. Some of the savings (about $750?) came from the recommendation of using the 95% carrier comfort furnace (58MVC100-120) vs. 98% Lennox that the Costco contractor quoted. The Carrier contractor said that 98 was probably not worth the added cost in our situation. Both suggested the 14 SEER single stage was their recommendation. Both mentioned that the 16 SEER 2-stage A/C would not pay for itself in cost, but would save some electric and also provide for improved de-humidification even if the indoor temp setting is relatively high. So, it was quoted as an option. Apparently, the Carrier system integrates this all with the controllers? The carrier comfort systems quoted were 24ABB348 and 24ACB648. Both contractors said they would install a direct pvc outdoor intake/return system. The Carrier contractor noted that the lack of this and other aspects of the current design is greatly limiting airflow that ultimately is causing the upstairs zone to get much less air, especially at the end of the attic duct. As a side note, we are also in the process of getting quotes for attic insulation that will also seal/insulate the run up there which may help a bit also. I'm more impressed with the Infinity system, especially since the cost is considerably less. My only question that I will ask the contractor is that the Comfort line A/C units don't indicate that they are for use with the Infinity control system, as opposed to the Inifity series and some Performance models. Is that an issue or just marketing? They both seemed to quote about the same size AC and furnace, perhaps my measurements are off?

jbaker what is your fuel source for your hydro system? if you are satisfied with the operating cost and comfort of the hydro system, I see no reason to add a furnace. I would prefer that the air handler be located in a basement utility room over an attic location. If you are going with one system for all three levels, then I would want zoning controls for the three different zones. And if you decide to go zoning controls, then Bryant Evolution or Carrier Infinity is the way to go. They have the best single cource residential integrated control on the market. And you could consider a high eff heat pump system over straight AC especially taking into consideration your location/climate. I would get a couple of quotes. you need more returns on top and main floors for best airflow and overall comfort. ask quoting dealers for recommendations. finished basements at or partially below grade with reasonable insulation qualities have relatively low cooling and heating loads. IMO Good Luck!

As others have said ... the behavior during cooling depends on the individual system and how options that may be available are set. The first two houses and one apartment in which I've lived had systems that shut the blower off immediately. My current house (built in 2004, Carrier system) runs the blower for an additional couple mins. All the systems at the business where I've worked (three systems 30+ years old, one 2 years) shut the blower off immediately. The coil will not freeze-up if the blower stops. Heat extraction/transfer stops when the compressor shuts off so the coil will not get colder than it is at the moment the blower stops running.

20' can easily be accommodated, I've put in systems before with in some cases line sets as long as 100'. Just realize long line set runs require extra work and line set length requirements are not just length but also rise / drop from where the condenser sits. Yes piping, electrical wires etc. will have to be run to the condenser. The longer the line set run, you may minimize your choice among brands as some brands allow less in the amount of length / drop / rise in the line set. But at 20' total length any brand can handle that no problem provided the equipment is installed properly. If this is moving your AC condenser from current location you should NOT reuse the current line set in any fashion. Replace the whole thing to proper size. The HVAC contractor you choose should be well versed in things such as this, otherwise serious problems could follow.