I have a 100 amp main panel. I want to add a sub panel to increase the available power to run an HVAC system (total of 60 amps, 30 for the air handler with heat strip, 30 for the heat pump). There is an “available spot” on the main panel for a breaker to supply the sub panel. I have “heard” that the breaker supplying the sub panel can be rated at 50% of the load required by the sub panel. Is this correct? The main 100 amp panel already has breakers totaling 180 amp, one of which is oversized (a 70 amp breaker for a stove which I believe should be a 50 amp)….Additionally, there is currently a 2 pole 30amp breaker in the main panel that powers a Window unit AC which will no longer be needed.

So, basically of the 180 amp total of the current breakers, I would be down sizing the 70 amp breaker to a 50 amp breaker, removing the 30 amp breaker for the window unit which would make my new total breaker value in the main panel 130 amps.