There are many ways to define the term energy use efficiency in the ventilating fan industry and everyone seems to choose the one -high or low- which supports their particular argument for buying or not buying. Use 240V motors not 120V to increase energy use efficiency. Do not use hp or amperage to compare fan efficiencies. Fan energy use efficiency can be determined by dividing the cubic feet air/min by the wattage. Simply look at the cfm/W rating; the higher the cfm/W, the more efficient it is.