Look at rating plate on side of unit for Volts, Amps, Watts.
Volts x amps = watts.
If unit is 240Volts, then you need double-pole 240Volt breaker
If unit is 8500 watts at max power, then 8500 watts divided by 240Volts = 35 amps.
What size breaker for 35 amps?
When electricians figure load rating for breakers, they use the 80% rule.
40 amp breaker x 80% = 32 amp safe maximum load for 40 amp breaker. Use 8 gauge wire with 40 amp breaker.
50 amp breaker x 80% = 40 amp safe maximum for 50 amp breaker. I use 6 gauge wire with 50 amp breaker.
60 amp breaker x 80% = 48 amp safe maximum for 60 amp breaker. Again, use 6 gauge wire with 60 amp breaker.
How to connect wires to unit.
First of all, all outdoor HVAC units require power cut off located next to unit.
This lets the mechanic, or service tech turn power off to work on unit, even if the mechanic does not have access to main breaker box.
Next, open unit to see where wires connect.
If unit has wires, then connect both hot wires from 240 breaker to the wires inside unit. Connect bare ground wire to green ground screw.
If unit has terminals. The terminals will be labeled L1 L2. Connect each hot wire from 240Volt breaker to either one of the screw terminals. Then bare ground goes to green ground screw.
Copy following links for basic illustrations connecting wires to terminals, and to breakers, and selecting wire size.
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html
If you need further help, I’m available over the phone at
https://www.6ya.com/expert/gene_9f0ef4df2f9897e7
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