1. since the first unit is doing both the basement and first floor, isn't that 3200 sqft, not 1600? Granted, the basement won't need as much cooling but it will need heating.

2. I agree going with a variable speed blower and a higher SEER AC. 2-stage AC may or may not matter with the variable blower in that you will still get good humidity extraction at the lower fan speeds.

3. I'd like to see the ManualJ and what temperatures they assumed for summer/winter both inside and outside.

I question both sizing and selection of equipment models.

I would want zoning controls for basement and first floor. Definitely two stage var speed furnace for that system.

I also question placing a high eff condensing furnace in the attic for second floor considering Chicago area location. I would want to hear what dealer has to say about freeze-ups. Of course building quality and insulation quality play a factor here.

You should start by insisting on a written load calculation for both heating and cooling.

IMO

You need to find a new HVAC contractor. I would be suspect of a professional who has proposed 180K BTUs of heating and 7 tons of cooling for the house you have described. Cutting those numbers in half is closer to the correct value.

Find a contractor who will do a Manual J load calculation!

Are you planning to insulate the attic? If not then I would install bought furnaces in the basement. Basement should have its own zone if you really want to control the temperature in the winter.

If your windows are tight then you probable don't need a humidifier. You certainly don't need two.

Get smaller equipment and put the money towards upgrading to 2-stage furnaces and condensers.

agree with above posters.
get more bids.

pairing high efficiency heat with minimum efficiency
cooling doesn't make sense.
heat pump for second floor would make sense
as heat from first floor will help to heat.

two stage always above single stage for comfort.

if this company did a load calc..they fuged some
of the inputs. usually air infiltration is entered
as leaky, or insulation values are lowered.
lots of ways to tinker with load required.

good windows..but more detail on insulation
& air sealing details needed.

best of luck.

Thanks for the input, I have requested ManualJ from two different contractors. The objective is to have right load (likely smaller) equipment and used the money towards upgrading to 2-stage furnaces and condensers. We will see what come back with their update

The builder is putting good insulation (I think it's R45) in the attic to address freeze issue for the furnace.

I will request two zone for the basement unit.

Chen

You misunderstand my point about freezing in the attic. R-45 in attic floor is fine. But the furnace will still be in an unconditioned attic unless you take additional measures. You should discuss this further with dealer.

I would want a two stage var speed furnace for first floor and basement. Insist on zoning controls.

For second floor, you could go high eff single stage furnace but insist on the AmStd equivalent to Trane's XT series that has high eff blower.

IMO

IMO,

Thank for your suggestions. Can I ask you why your think second floor, high eff single stage furnace? Want to understand the "single stage" part. Thanks