However, just to be clear, you can't change out the breaker to match the unit if the wire sizes are still too small. Can anyone advise what sized breakers should I get installed (I am assuming most of the 5 TON AC's will have in same range). It has the same inputs as the whole house one, except it is done for each room. Take the total amount of square feet in your home. The wire gauge needed will be in the instructions with common sizes for mini split units being 10-12 gauge. 6. Checked main breakers for both units and breaker on air handler. It does not take into consideration any of the specific factors that can really impact AC size needed for a particular house. The only reasons you don’t want a larger size unit is because it costs more upfront.