As said before, the numbers are inflated. If you convert how much power can be drawn out of the wall, a 15 amp circuit can only supply 2.3HP, and a 20 amp circuit can only supply 3HP. That's 100% efficiency. Take into account the losses in the electric motor, conversion into heat, the friction in the pump, the pumping losses, and you get much lower power, so HP cannot be used. Also, the CFM at a certain pressure are at 100% duty cycle. The compressor usually must be used at a lower duty cycle, like 50% on and off, so that CFM must be cut in half if used for any length of time.