From About This Project
If the grille on your bathroom exhaust fan is clogged with dust, try a trick that’s faster and more effective than vacuuming: Turn on the fan and blast out the dust with “canned air” ($5). The fan will blow the dust outside. This works on the return air grilles of your central heating/cooling system too. Run the system so that the return airflow will carry the dust to the filter. You’ll find canned air at home centers and hardware stores, usually in the electrical supplies aisle.
CAUTION: The cans contain chemical propellants, not just air. Don’t let children play with them.