Proper maintenance of both fireplace and furnace chimneys should be an annual occurrence.  By having a CSIA certified, (Chimney Safety institute of America) chimney sweep routinely inspect and sweep your chimney you insure the safety of your family.  Also, when you have a trained professional looking at the interior and exterior structure of your chimney, future problems can be found before they become life threaten, or cause extensive damage to your chimney structure.  Cleanings and inspections are preventative maintenance for your chimney, but sometimes an ounce of prevention is worth a pound of cure.