Depending on the geographic area, the complexity of the job, on new construction somewhere between $5000-9000. If in existing building, maybe additional $3000-5000. I am using Payne as a price basis. Payne is a Carrier brand. Carrier is more expensive but not more than 20%. I did 80% install earlier this year with used equipment. It was less than $1500 total. It was a 2 1/2-day job, with new lines, rework to gas line, added 2 vents, new exhaust thru roof. Built custom plenum. All in all, it was only 2 1/2 days. I am fat, old and slow. Under better conditions I should have completed the job in a day. $20k is a lot of install for a 3.5 ton system. 5 tons sounds like Pheonix or Florida. Your contractor did not do a man J in all probablilty.

The house will be in humid Arkansas. Dealer recommended 5 tons b/c the house has a lot of windows in the front, a vaulted ceiling over the living/dining rooms.

It looks really high compared to what we paid for 2 Infinity stats, 2 64k Infinity VS 80 furnaces and 2 Performance 13 SEER 3 ton units, in new construction 2 years ago.

Dump the Performance furnaces and get Infinity -- the VS married to the Infinity t-stat will be the best for humidity removal. You could easily get a 13 SEER or 14 SEER and have no issues that way.

I was just quoted two carrier infintity systems both 3 tons with 17 seer rated heat pumps, these are complete infinty systems with 10 year warranty installed in new construction with duct work and all the fixins for $12000. Now, the catch, these are scratch and dent systems with no defects other than they cant be sold @ new cost,other than a dent and scratch there is nothing wrong with either system. If i go with two new systems add 6k to the 12k to me its a no brainer. I was going to go with two trane systems originally but @ 21k I just couldnt swing it.

we sell the Carrier Infinity 21 systems at whosale price
and depending on size it starts for a 2-ton system changed
from the old to the new for $7498.60 parts and labor and the 5-ton carrier infinity 21 changed out for as low as
$8998.60 that is the special we run on ebay everyday .
866-289-3909 we sell and install everywhere.