Chimney cleaning should be done regularly. Inspections find chimney leaks that occur from stonework integrity, not based on how often you use the fireplace. Both the Chimney Safety Institute of America and The National Fire Prevention Association recommend a yearly chimney inspection to prevent fire hazards.
Bird nests and other obstructions can cause chimney fires and carbon monoxide poisoning. A visual inspection of the chimney flue may reveal cracks or other structural problems that should be addressed before the next fire.
Another problem in the flue could be a buildup of creosote. Creosote forms when wood does not burn completely. Natural chemicals in wood vaporize and drift up the chimney. These chemicals and water vapor from the burning wood condense on the walls of the flue. The more creosote that collects on the flue, creates a greater the chance of a chimney fire.
According to Dan, from Pointe Chimney Repair, there are three stages of creosote. First, the dusty or ash residue, then crusty like burnt molasses, then shiny hard like candy. The first two are easily cleaned with brushes. The third stage, shiny hard, requires chains or chemicals to clean the flue.
Ways to reduce the buildup of creosote begin with burning dry seasoned wood. Wet or unseasoned wood provides moisture, adding to adhesion and formation of creosote. Keep fires small; the greater amount of oxygen supplied to a fire, the better the wood is burned.
Using a woodstove or a fireplace insert can increase accumulation of creosote. Slowing down or smoldering a fire for extended periods also increases formation of creosote.
An open fireplace flue should be inspected yearly and cleaned about every three years. The flue for a woodstove or other device that allows the airflow to be restricted should at least be cleaned yearly.