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?

Thanks guys for the comments. I just want some professional advice before I make my final decision on the furnace. I know the best choice is a variable speed, 2-stage but nobody makes them in a 45K 80%, period. They are all 65-70K or bigger. Bryant makes a 2-stage 45K (312AAV) but it only has a bad old PSC motor. I could ask the installer about replacing the PSC motor in the 312 with a 'green' variable speed motor (www.evergreenmotor.com) as he gave me a brochure on it, but replacing a brand new motor doesn't sound very wise. The Bryant 313AAV has an ECM (X-13) motor but only a 1-stage 45K burner. I looked at the spec sheet on the Trane XV80 (somewhere on the net) and the smallest size I saw was 60K, no 45K model in the XV80. Did I miss something? I know probably the low stage (32K) of a 45K 2-stage burner would likely be sufficient 90+% of the time. The furnace usually runs Nov-Feb and perhaps a bit in March depending how could it gets. This past March it never ran at all. During April, May, Sept and most of Oct. i rarely use any heat and not much AC in Sept. The condo mgmt. sent out a notice last year that if our condenser units needed replacing, that we would have to replace our evap. coils at the same time (the coil would be at our expense-$400-$800, the condenser at theirs). I figured it was because the new condensers would all be R410 and the old R22 coils in current use would have to be replaced. the installer said he would replace my coil with a R22/R410 compatible unit so I will already be taken care of when the condenser finally fails. Yes, I thought on my own that the new coil might be too much of a strain for the old condenser. However, if I want the condenser replaced now I have to pay for it. As long as it is working they will not pay for a new one, even if I am getting a new furnace and coil.

I was able to get info on the existing furnace from the data plate. It's a Carrier Model 58ss140-BC, Series 110, 167,000 BTU. The data plate said the blower is "157", whatever that means. The motor spec was 1/2 hp. Mfg date 1982. That's all I found on the furnace. I found next to nothing on the a/c. The data plates outside are gone. I could see where it was but there was just rivets. A single, long rectangular unit outside. Like I said, vintage 1974, from the builder. According to my mother, the quoting contractors guessed that the system was 4 or 5 tons. I don't know anything about who said what. Turns out the Lennox/Costco guy was the only one to quote an upgraded unit. He also quoted: Option #3B. $9,185. Platinum Package. A/C XC17-048 and 2 stage gas furnace SL280UH135 with variable speed and I-Comfort Communicating Controller. I'm having a hard time getting her to look at the Am Std quote because they didn't quote her an upgraded unit option and their basic units were only about $1,000 cheaper than the upgraded Lennox units. ($9,145 vs $7,945). About the house, I tried to describe it above. Built 1974. 3200 sq ft. and two stories. Attached garage. Full sun exposure--the property is not shaded. Brick exterior with not a whole heck of a lot of insulation. (I remember my parents being mad that the builder gipped them on the insulation.) High quality house though, expensive neighborhood. Stick framed over a full basement. Attic with pitched shingle roof. Colonial. Original single pane wood windows with storms windows, maybe a tad drafty. After being widowed with 4 kids in 1978, she never had the money to remodel anything and everything is pretty much 1974. Anything else you want to know about the house, please ask. This is all I could think of.

With help from the forum, I got 3 consistent load calculations and a bunch of quotes. I have settled on the American Standard contractor who was knowledgeable and had a fair price. Here is my final choice: AUD2C080B9V4 4A7A7048A1 4TXCD063 AHRI# 5942858 I am going to add a 5" media cabinet as recommended here. TFM245B0FR0. The contractor recommended getting the largest filter (24" wide) even though the furnace is 21" wide (said it improves air flow). My last question deals with the thermostats. I've read all the forum posts and am still a little confused. I've asked for a quote on the Honeywell Prestige IAQ 2.0 as recommended here. The contractor is recommending 803s, however. Should I insist on the Honeywell? The contractor made it sound like the 803 does the same thing but from reading here it seems like the 803 just overcools to de-humidify whereas the Honeywell slows the blower speed. Is that correct? Is it possible to have one Honeywell Prestige downstairs that controls both the downstairs and FROG (with a temp and humidity gauge installed in the FROG)? Let me know any final thoughts before I sign the contract. Thanks so much. MB