One BTU is approximately 0.000293 kilowatt-hours. To convert BTU to kWh:
Take your BTU and multiply it by 0.000293.
Multiply by the air-conditioner operating time in hours.
Let's say that you have a 12,000 BTU air conditioner running for 6 hours per day. It will use 3.517 kilowatts of energy per hour and 6 hours × 3.517 kilowatts = 21.102 kilowatt-hours per day.
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