Even when you rarely make a fire, creosote can build up over years or if you have never made a fire in your fireplace, creosote could be inside the chimney from the previous owner or tenant.
"I use my chimney very rarely, why should I worry about creosote"
What Is a Chimney Fire?
Once there is sufficient creosote buildup, the highly combustible creosote inside the chimey can be ignited by a regular fire in the fireplace, causing flames to shoot out of the top of the chimney. The temperature of a chimney fire is at least 2000 °F or higher. A regular chimney cannot withstand this high temperature, therefore the outside wall of the chimney will be hot enough to ignite combustible materials around the chimney. In most cases, the walls of the chimney will break from the inside out, and while many chimney fires stay contained inside the chimney liner, it is not uncommon for a chimney fire to become a structural fire as well. Chimney sweeping is the primary defense against chimney fires.
The average chimney fire will make a loud roaring noise, often described as a train or jet going through the home. The roaring noise is caused by the sudden rush of air going into the chimney to feed the fire and a column of flames will often be seen coming out the top of the chimney.
Pieces of creosote will often be seen flying out the top of the chimney and these may ignite the roof or other nearby combustibles. You may also hear popping or cracking noises inside the chimney indicating damage to bricks, mortar and flue liners. In some cases, a dense black smoke coming from the chimney is the only indication that a chimney fire is in progress.
The National Fire Protection Association (NFPA) recommends chimney inspections once a year and maintenance and repairs done if necessary.
The Chimney Safety Institute of America (CSIA) recommends sweeping if 1/8” or more of soot or creosote is present anywhere in the chimney system.