text: how many watts are needed to power an office 2.5 horsepower airconditioner? the airconditioner will be in use for around 10 hours daily yes, 1865w via direct conversion...but its important to remember that the compressors in a/c systems are very high inductance, so the voltage waveform leads the current waveform quite a bit, and lowers the power factor. im not sure how many more watts (its gonna be 100s) the system would use since i dont know the motor specification.  the best way to determine the power usage is to read the rla (run load amps) off of the compressor, and multiply that by the input voltage. this still isnt too great of a way, but its better than an hp conversion for sure.   if the compressor only lists the lra (locked rotor amps, current flow at 0 back emf), divide that number by 5 for a rotary compressor (cylindrical) or 4 for a hermetic sphere compressor (egg like) to get the rla. doing this further decreases your accuracy of course.   hope all this helps