A lot of people don’t know it but not all chimney fires are the same, that is, professionals classify chimney fires into two different classes based on differences between the two, and both are generally covered by homeowner’s insurance. You will want to check with your insurance agent to be sure that you are protected against both. The difference between the two is the way the fire actually burns.
A rapid burning chimney fire is the type of chimney fire which your chimney professional will usually detail to you. An rapid burning chimney fire can be characterized by a loud rushing or rumbling sound which can resemble the noise of a nearby freight train. Insurance agents refer to chimney fires as sudden occurrences.
Chimney fires are caused by creosote buildup in the flue system which is ignited by sparks from the flames below.
The rapid increase in temperature in the flue system caused by combustion can cause physical damage to the flue system in the form of cracking the flue tiles or even causing them to crumble. These types of chimney fires generally leave behind glazed creosote all over the flue system because combustion actually occurs in the flue system and the creosote is what is being burned.
A slow burning chimney fire occurs when the heat from the flames in your firebox, which is intended to contain such heat, makes their way up through the damper system into the chimney flue system. These chimney fires burn slowly due to lack of oxygen.
When certain conditions exist, the flames move up through the damper system from the firebox, causing an extreme change in temperature in the flue system known as thermal shock. This thermal shock can damage the flue tiles by cracking or crumbling the flue tiles which are not meant to contain such levels of heat. In slow or rapid burning chimney fires, sometimes the chimney’s flue system is completely cleaned so that it looks like new. This is not typical but can be the result of a chimney fire.