A box fan is simply a set of fan blades attached directly to the shaft of a small motor. An oscillating fan includes a gear assembly that swivels the fan.
Box fans are best used for exhausting hot or stale air from a room. In contrast, the swiveling feature of an oscillating fan can also be set to exhaust air, but it usually can't move the great volume of air a box fan does.
A problem common to both types of fans is excessive noise.
Accumulated dirt can cause noise because it can unbalance fan blades and wear out bearings. After every two weeks of use, vacuum a fan with a crevice-cleaning attachment. At least twice during the summer, wipe dirt from the blades with a damp sponge.
Check to see if there are external parts that are loose. Inspect fan guards, decorative emblems and the housing for looseness. Check to see that the fan guards are firmly attached to the fan housing. If the blade guards still rattle, try wedging a piece of cardboard between their edges. If the decorative cap on the front guard is noisy, secure it with a drop of silicone sealant.
If rattling persists, disassemble the fan and check for loose internal fasteners.
Newer fan blades are usually made of plastic, older ones of metal. The hub to which the blades are attached may be friction-fit to the motor shaft or secured to it with a C-clip or a hex setscrew. Wear goggles when prying off a C-clip to remove the hub. The metal blades on older fans may be secured to the motor shaft with a setscrew on the back of the fan hub.
A whirring sound may indicate that metal blades are out of alignment or damaged. To realign metal blades, unplug the fan and remove the blade hub. Place the hub on a flat surface. Each blade should touch the surface. Measure the height of each blade. If heights vary by more than a quarter of an inch, bend the blades to align them, or replace the entire assembly.
Plastic blades can't be repaired, but on some fans the blades are attached to metal brackets that can be bent to bring them into alignment. Check the plastic blades for cracks; replace them if necessary.
Plastic blades are secured by a spinner that unscrews like a nut. Tighten the fan hub to the shaft by tightening the spinner that holds it in place. If the spinner loosens repeatedly, secure it with a drop of thread-locking compound, available in hardware stores.
Is the fan poorly supported? Replace any pads that may be missing from the base. If the fan runs quietly on a cushioned surface, the rattle may occur if the surface on which the fan normally rests is not level.
Most fans today have a sealed motor that does not require oiling. If the motor on an older fan has oil ports, lubricate the motor and shaft at least once a year. Use SAE 20 non-detergent oil and apply no more than two drops to each oil port. Be cautious when lubricating. Use lubricant sparingly to prevent motor damage.
Always unplug a fan when it's not in use or before cleaning or checking it. Don't leave fans running near unattended children or pets.