I want to install a dedicated circuit for a 110V 12000 btu window AC.
I want to run a 20 amp circuit, mostly because I already have a 20 amp breaker, 20 amp outlet. 12 guage romex, but also because even though the specs on this AC say 15 amp, I think that's pretty minimal for a unit this size.

20 amp OK or should I just go ahead and make it 15?

 

Install the 20A circuit. The 15A circuit requirement on the A/C unit is the minimum. If this receptacle is the only receptacle on the circuit, then it must be a 20A receptacle. A 20A receptacle has a "T" shaped slot instead of the usual smiley face shaped 15A receptacle.

 

Don't worry about the receptacle. Just use a regular duplex receptacle. As long as it's a duplex, it can be a 15 amp receptacle.

 

I dont believe you can assume a minimum on a window a/c, they're not treated the same as hard wired central air. The rla x 125% is already factored into the nameplate rating and a branch circuit size is stated not a minimum circuit ampacity. I suspect it will fall on the 50% rule and require its own circuit with no other loads. Most window air that are 12000 BTUh are 10 or 11 amps provided they dont also have a heater. It also is rated at 110v 15 amp it appears so it has a 15 amp cord and is intended for a 15 amp branch circuit. And should work fine on a 15 amp circuit. I dont see any reason to not run the #12 awg wire but I would still breaker at 15 amps. Only about $4.50 for a 15 at the home centers. Yes it will plug into a 20 amp receptacle but that is not the intention of the manufacturer.