Do I need 10/2 or 10/3 wire for a 220V heater?
Your load is 20 amps so you should use 10 awg.  Heaters are continuous loads, to size the wire correctly it is 125% of 20 amps or 25 amps. The fans usually run on 120v and they would require a neutral 10-3 with ground would be the proper wire.