For motors it's .7, it has something to do with the phases being out of sync. This is what your meter will read.
Watts x Pf x time / 1000 = KWH
Now the circuitry hasn't been factored in either. I'm sure it isn't much but it all adds up. Still a very efficient unit for what it accomplishes. The pump size needed to run one of the screen/vortex ones will use more power 24/7.
Garrett