I want to run copper wire from my 200Amp main electrical panel to a 100Amp sub-panel. The 100Amp panel will feed a heat pump compressor, air handler with heat strips (total load = 70 amps) and about 4 20 amp outlet lines. I have previously wired a 60 Amp sub-panel in this house.
The panels would require about 12 feet of wire from one to the other.
What size wire should I use for the 100Amp panel?

#4 copper is the min size allowed for a residential 100 amp feeder.