Need Help Comparing Different HVAC Options

[Guti12]

I have gotten several estimates for new HVAC equipment in my 3 bedroom ranch style house. Current system:

2 ton carrier AC unit ('91)
3 ton ADP coil ('06)
80,000 btu trane xp 80 furnace ('07)
Current duct work is mostly in the floor, but for a bathroom, and converted garage, duct work is through attic.

Any thoughts on which replacement system sounds best would be appreciated:

proposal #1:
2 ton carrier perfom. 16 #24ACC624
carrier (80% efficiency) furnace #58CVA070-12
2 1/2 ton coil (#cnpv3014)
new supply ductwork in attic (flex duct w/ metal splitter)

proposal #2
3 ton carrier ac #24ACC630
3 ton coil
carrier 80% furnace #58CUA070-12, 70,000 btu
infinity thermostat
no duct work

proposal #3
Trane XV80 furnace, 80,000 btu variable speed
Trane 2.5 ton XL15 air conditioning
3 ton Trane coil
no duct work

I am most confused why each company comes up with a different size air conditioner and coil, and why the btus on the furnace vary. I have asked about Manual J calculations and have been told they do not do them because they are too expensive ($600+) and too many uncertain variables, like wall insulation.

[BaldLoonie]

2, 2.5 and 3 ton. Wow. How has the current 2 ton been? If you go 50% larger, ask that fine dealer why he isn't increasing your ductwork and number of registers by 50%? Chances are, what you have is barely big enough for the 2 tons. So I sure wouldn't go bigger without adding to the ducts. Furnaces are close, Carrier has 70, Trane has 80.

Sad they are feeding you with such bull#$#! about manual J's. Buying a program does cost some money but will accurately tell what size equipment is needed. The estimator plugs insulation and all the factors that go into it into the software and it spits out the right size. Or it can be done by hand with a pen and special form. Nobody should be out there in biz that feed a prospective customer this crap. I wouldn't guy from any of them. It's your comfort and utility bill for the next 20 years at stake.

For $50 you can download HVAC-Calc, register it and do your own if you can't find a dealer willing to do things right. Sad that a HO has to stoop to this but many have.

[kdean1]

Too expensive? I can measure a house in 1/2 hour or less and enter the data for the Manual J in another 1/2 hour. Add an hour for drive time to be generous. They're WAY off base. I advise you to reject any contractor who tells you that.
Call other contractors and ask them if they perform a Manual J BEFORE inviting them to look at your house. They may do very nice work but be too lazy to spend time on a load calculation. Of course, one of their guesses might be right, but do you want to take the risk? This is science, not guessing.

Most manufacturers make good products but your contractor should be able to prove to you which ones will be appropriate for your house. Then you can choose if you want such options as a variable speed blower and a two-stage or modulating furnace or just the basics.