Answer by Josie74 (225). It depends on the size of fan, but for a ceiling fan running on high for 24 hours a day would cost 41 cents per KWH or $6.15 a month.t will depend on the age and size of the ceiling fan you have running. However most home ceiling fans, even when left on 24 hours a day, will hardly reach 5 dollars a month to run. If you find that you can remain cool using a ceiling fan instead of the AC running, you'll end up saving money quickly.