from what i understand, normal `household` fans are not designed to run for the lengths of time required in a grow room.
Ive read about household fans even being responsible for causing fires due to the fact they are not designed to run constantly.
I use an 8" bionair industrial fan,only cost me £45 but its designed to run continuously and shifts a lot of air,only drawback is they are slightly noisier but if your room is tucked away this shouldn`t be a problem.
Well worth $45 if you ask me!