Looks to me that both furnaces are oversized.

Even the second floor condenser is oversized. They do make 1 1/2 ton AC condensers.

I would take a chance on a 60 K mod furnace for downstairs system.

You may want to review your calcs again paying close attention for design temps for your climate/location both inside and outside, cooling and heating.

BTW, where will furnaces be located? You normally do not place high eff condensing furnaces in an attic except for location with mild winter.

IMO

"Knowing a house" is not a substitute for doing a Manual J calculation. This is another way of saying "I don't want to be bothered".

I think your first floor furnace is over sized. A 60K BTU furnace will be more than adequate. I don't understand why your second floor heat loss is so much less than the first floor. What insulation did you enter for the attic?

I also question how the second floor heat gain can be less than the first floor. The second floor gets a lot a heat from the attic.

Why is the contractor recommending a single stage units for the second floor? Is it to save money or he thinks it will work better than a 2-stage?

How what did you use for your average high and low outdoor temperatures? What are your indoor design temperatures? Are you getting a 2-stage thermostat for the first floor?

To answer the first reply, the upstairs furnace is to be installed in the attic. Our winters are typically mild with average highs of 45 and lows of 26. But we definitely have lows down to the mid teens from time to time.

The design conditions I entered in HVAC Calc were:

1) Outside temps summer 89, Winter 14, summer grains of moisture 92, daily range medium (taken from their list of default temps from a nearby city to me)

2) Inside design temps summer:75, winter 72 degrees, 50% RH

Attic insulation is R-38

The single stage upstairs was just to save money and because I was more concerned about dehumidification in the main floor/basement hence the two stage A/C.

I intend to get a 2 stage thermostat for the main floor/basement.

Thanks again for your feedback.

With some brands, you will find it difficult to get sized correctly for your upstairs furnace assuming your heat loss calc is accurate.

What is size of living area for upstairs?

Post back.

IMO

I'd do a 2 ton single stage for each floor. If you install a 3 ton downstairs it will never hit 2nd stage, which means you have spent double the money for nothing. How much of the 27,000BTU 1st floor heat gain is from appliances or unshaded windows? Simple solution is to use common sense and close blinds/reduce appliance use on the days when it's 90+ outside. I also have to question the 7,000 heat gain from the basement, basements generally are cool even when no AC is used.

FWIW I have a 2 ton on my own 1600 sqft single story house it it will keep it 75 inside on a 100 degree day. Typical construction for a 14yr old house, but the AC is installed RIGHT.

http://acrightsize.com/files/7_reasons_why_oversizing_is_a_bad_idea.pdf

Instead of getting a 2-stage compressor for humidity removal, get a single stage with a variable speed blower. Should cost less and still be effective.