Just this observation.

Your existing furnace is oversized. Very typical then and now.

I would want a 95% eff furnace, 2 stg var speed, probably 80K size.

Get a load calc for both heating and cooling. Keep in mind, finished basement living area at or partially below grade have low heating and cooling loads.

Go ahead and start securing quotes now.

IMO

Thanks, tigerdunes. Any other input on brands, models, types, sizes, etc would be greatly appreciated!

The best brands are Carrier/Bryant, Rheem/Rudd, Trane/American Standard. I also suggest a 95%+ efficieny furnace for your Chicago area winters. If you have humdid summers consider getting a variable speed furnace and a 2-stage AC.

If you have the funds then do a complete matched system installation. Wait until the hot weather has ended and the before the cold weather has started. HVAC contractors will be less busy and have time to answer your questions. The rebate season also starts after Sept. 1.

Get a load calculation. You seemed to be oversized. A good contractor will review the duct work for the temperature problems you currently have. Get 3-4 quotes preferably of the same brand family. Stay away for the low end equipment.

Is Lennox competitive? I noticed Costco contracts with Lennox dealers for their "Signature" and "Elite" lines.

There seems to be mixed opinions about Lennox. I have never fully understood why people don't like the product.

There is no advantage in going through Costco to buy an HVAC system. The contractor has to share the profits with Costco, or charge a higher price.

Costco is giving 10% back in a cash card, plus the extra 2% cash back for executive members. If the prices and quality are comparable, that could be the difference. Obviously if the markup is 10-12% for Costco's cut, that would negate the difference, but no harm in getting a quote unless Lennox has some major issues.

We recently bought a Lennox signature 21 through Costco. We got $900 cash card & 2% for exec mem. Costco guarantees it in addition to the installer. I am very happy with the unit. During the very hot days my house was very comfortable. We generally keep it at 76.

Costco's contractor finally got us the quote. It included a 110k btu 98% lennox signature gas furnace (SLP98UH110V60C). With the 4-ton, 16 seer dual stage lennox elite condensor (C16-048-230) and a harmony III zone system, the cost was nearly 17k. A utility rebate, cash rebate and cosco rebate dropped it down to 15.6k. This included furnace, condenser, coil, humidifier, lines, thermostats, 2 service calls, new pad, all connections/installation, etc. Stepping down to the single stage 14 seer Lennox Merit condenser saved almost $1500. Either way, it was way over what I was expecting so I will certainly get another quote. Any comments?

Oversized on heating side and I do not recommend purchasing HVAC through a third party big box store like Costco.

Let's see what other quotes look like.

IMO

The price seems high. You can do better going directly with a reliable HVAC contractor. Did the contractor explain how he is going to address the problem with one of the bedrooms?

Agree with others, go straight through contractor. 3rd party tends to find the cheapest guy who will take the job. The best contractors don't need the work through 3rd party.

SEER 16 or higher makes no sense above the mason-dixon line. Stick with a 14-15 SEER, downsize to about 2 tons. 80K sounds high for a furnace, are you OK with a $300 gas bill? If your house really needs 80k, your bill would be that much.

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?

I have the Carrier Infinity 58MVC furnace. It has worked very well for me so far. I believe the Comfort AC is compatible with the Infinity controller. If you have high humidity in your area you should consider the 2-stage Infinity AC. It is worth the money in my opinion.

There are 2-stage performance and infinity AC units with similar efficiency that are listed as compatible with the Infinity controller. Anyone know what advantage these provide over the 2-stage Comfort model, assuming it can be used with the Infinity controller?

Costco/Lennox Quote was $13.8k after $1k in Costco cash and $450 in rebates for XC14-048-230, SLP98UH110XV60C and Harmony III control system. I felt 4-ton single stage and 110kBTU was too high, cost was too high even after significant rebates.

Never did get a response to my calls or emails from contractor #2 about the AC unit compatibility or about some vague aspects of the quote that didn't seem to specify the Infinity control system, dampers or thermostats. Price for 24ABB448 and 58MVC100 was decent at $10.2k after $1500 in rebates, but wasn't happy with lack of answers about stepping down from 4-ton single stage to 3.5 or 3-ton and also some other missing details on the quote.

A third Carrier authorized dealer quoted $12.7k after $900 in rebates for 58MVC100 and 24ABB348 with Infinity controls. Not sure why they also quoted 4-ton single stage unit, even though they clearly said they thought only 3 or 3.5 ton was needed and also said return airflow was not sufficient and would have to be increased to support 3.5 ton anyway.

Due to all the conflicting information in the quotes, I ended up with option #4. Finally had a family friend that does HVAC for a small company quote a Carrier Infinity system with 58MVC100, 24ACC642, CNPVP4221 coil. Essentially got equipment at distributor cost, but since they weren't authorized for Carrier, did not get any Carrier rebates. Cost was $8.8k after local gas company rebate of $250. System now installed, will know if it resolves airflow problems in a few months. They did add some return airflow and we also insulated the attic recently, so hopefully it will be nicer, cheaper and more reliable.