Somewhere on the data sheet/install instructions it should state the current draw. Pay attention if there is a "startup" rating as well. All electric motors draw a larger amount of current while starting up, then taper off to "running" amperage.
If it's not listed, do an experiment. Start with a 5, and go up in small increments. Stay with the lowest rated fuse that'll live, and possibly then go with a "Slow-Blo" type.