Disconnect the box fan power cord from the wall outlet. Place the fan on its back and remove the screws securing the front cover grill with a Phillips-head screwdriver or nut driver, depending on the screw head.
Fill a small container with a 50/50 mix of white vinegar and warm water. Dip a cloth into the mixture and wipe down the front cover grill. Use the corners of the cloth to get in between the grill and remove as much dirt and dust as possible. Wipe the grill clean and dry with a dry cloth.
Stand the box fan upright and go to the back of the fan. Spray compressed air around the fan motor, especially in areas that are open. This process removes the dust and dirt that clings to the motor as the fan draws in air from behind.
Go to the front of the fan and wipe down the blades with a cloth dipped in the vinegar solution. Wipe the front and back of the blades as well as the blade shaft. After you wipe the blades with the vinegar cloth, rinse the blades clean with a clean damp cloth. No dirt streaks should when the process is complete.
Wipe the rear cover grill and the outside of the box fan with the vinegar solution and a cloth. Allow the rear grill to air dry. Wipe down the outside of the box fan with a clean damp cloth.
Place the front cover grill over the front of the box fan, lining up the mounting holes. Secure the front cover grill to the fan with the retaining screws.