Why do some vacuums use watts and others use horsepower?
Watts is the measurement for power, so is horsepower. Power over time is measured in energy using joules, BTU, kilowatt hours or hp-hours. Watts is calculated my multiplying current (in amps) times the voltage. The average voltage in most homes is 120V. In reality, it is a volt or two less. This means that the most wattage one can get from a 120v 15 amp circuit is 1800 watts. This is not safe. The maximum “safe” device that can be used on 120v circuit is 13 amps, 1560 watts. When start they surge and need more “room”. A 13 Amp motor should be on a 20 amp circuit. 1 horsepower is 745.56 watts. 1560 watts is 2 HP. I do not know how companies are calculating horsepower for electric motor powered equipment like shop vacs and electric chain saws, these days, and can rate vacuums at 4 hp or 6 hp 120 volt circuits. If anyone has that answer please email us. I understand that the industry drove this new type of HP rating. Central vacuum companies are generally not using HP to rate their power
