Will my circuit handle this air conditioner?

Breakers are rated for the current they will carry indefinitely without tripping, but US practice loads a circuit to no more than 80% of its rating for a continuous load — anything running for three hours or more, which describes an air conditioner on a hot afternoon exactly.

• 15-amp circuit: 12 A continuous, about 1,380 W at 115 V.
• 20-amp circuit: 16 A continuous, about 1,840 W at 115 V.

That is the budget, and the air conditioner is not the only thing spending it. A bedroom circuit typically also carries lighting, a television, chargers and whatever is plugged in next door, because household circuits serve several rooms.

Room air conditioners publish CEER — the combined efficiency ratio, in BTU per watt-hour — for every certified model, so the running wattage is two divisions away:

Watts = BTU ÷ CEER, then amps = watts ÷ 115.

Worked through the capacities people actually buy, at the CEER levels certified units are reaching today. This is our arithmetic on published figures, not a manufacturer table:

The pattern is clear enough to remember without the table: everything through 12,000 BTU is a 15-amp proposition, and everything above it is a conversation with the panel.

A fixed-speed compressor draws several times its running current for a fraction of a second at startup — locked rotor amps. It is brief enough that a healthy breaker rides through it, which is why a unit can run for weeks and then trip on a hot day when the compressor restarts against high head pressure.

Two practical consequences:

• Repeated tripping at startup, not during running, is a circuit that is too close to its limit, not a faulty unit.
• An inverter compressor sidesteps it. Variable-speed units ramp rather than slam on, so the startup surge is small — one more reason they suit marginal circuits. The rest of that case is in inverter versus fixed-speed.

The plug on the cord tells you what the unit needs, and it is the cheapest compatibility check there is.

• Two flat blades and a pin (NEMA 5-15P): ordinary 115 V, 15 A outlet. Everything through about 12,000 BTU.
• One blade turned sideways (5-20P): 115 V but a 20-amp outlet. It will not fit a standard socket, by design.
• Both blades horizontal, or a different pin arrangement (6-15P, 6-20P): 230 V. This is not something to adapt; it is a separate circuit with its own breaker.

If the listing quotes 208/230 V, the unit is not going into a bedroom socket at all. That is normally the point where a mini-split enters the comparison, since it needs an electrician either way.

Manufacturers prohibit extension cords on room air conditioners without exception, and the reason is arithmetic rather than caution. A cord has resistance; resistance times current is a voltage drop; the motor compensates for lost voltage by drawing more current, which increases the drop. The cord warms, the plug warms, and the failure mode is a melted connector rather than a tripped breaker.

The same applies to power strips, which add another set of contacts and are often rated below the circuit. If the unit will not reach the socket, the answer is a different socket.

Finding out is a ten-minute job and it settles most of these questions. Switch off one breaker and walk the rooms with a lamp or a phone charger to see what died. Anything that goes dark shares the budget with the air conditioner.

The loads that matter are the ones with motors and heating elements: a space heater, a hair dryer, a microwave, a window fan is negligible by comparison at under a hundred watts. A 1,500 W hair dryer on the same circuit as a 12,000 BTU unit is 13 amps between them before anything else is counted — over the continuous limit and into breaker territory.