I need help with wire required for 3 ton units for my home heating. I am not sure if the units will be: all electric, fuel/electric or just what they may be when I can finally afford them to be installed, but the rest of my house is being held up by the wire required to operate the units. I have several different opinions and they all come back with 2-3 ton units to heat/AC this house, but no one will tell me what wire I need to run. A friend told me to install (2) 12-2 wires and (2) 6-3 wires. The 6-3 wire is my question... is that major over kill or is there a reason to ever need that? Will 6-2 for each unit due or can I even get away with 8-3 or 8-2??

10-2 to outside units
12-2 to the indoor if you go with gas or fuel oil or propane
If you go with electric units inside you will probably need 90 amps for a 15 kw heat strip. Usually a 30 10-2 breaker and a 60 6-2 breaker