Chimney Fires & High Heat Events
Chimney fires, although preventable, are not an uncommon occurrence. Our goal is to educate our customers as to how to prevent a chimney fire and what your next steps are if one occurs at your home.
What Causes Chimney Fires?
When you have a wood burning fireplace, the byproduct of combustion that we are most concerned with is creosote. Creosote is formed as the smoke travels through the system, cooling as it goes, and creates condensation deposits that include unburned wood particles. It will appear as a black or brown tar like residue on the walls of the chimney flue system, crusty/flakey, and will become shiny as it hardens. With each fire you have in your fireplace, the deposits will continue to build causing a glaze of creosote.
While creosote is one of the many reasons a chimney fire can occur, you also want to look out for other flammable materials that may be blocking your flue system. Uncapped chimneys welcome birds, raccoons, squirrels, and other critters as a warm place to build their nests. Nesting materials, animal waste, fur, feathers, and other debris can cause a blockage in the flue system and ignite, causing a chimney fire/high heat event.
Why Is This A Concern?
Creosote is not only highly corrosive to your flue system - due to the unburned wood particles that are deposited, it creates a highly combustible environment. When the flue system heats, it may ignite the creosote causing what we refer to as a chimney fire. While you may think it is your chimney’s job to keep the fire maintained within its structure, the truth of the matter is, it is not. Chimneys are constructed to lead smoke and gasses from your fireplace, not to withstand an actual fire in its structure.
What Happens To My Chimney In A Chimney Fire?
When you have a clay lined, masonry chimney, the temperatures that they experience can reach over 2000 degrees. This can cause thermal shock which cracks the clay tiles (if present), can melt mortar joints, can cause flues to collapse, and mortar to shift. The major concern, when this occurs, is to the surrounding combustible material where the chimney fire spreads to the surrounding areas in the home, creating further damage and risk.
Prefabricated or factory built chimneys are often required to be UL Listed to withstand heat of up to 2100 degrees Fahrenheit. Unfortunately, they can still be damaged by chimney fires or high heat events. Once these flue systems are damaged, they require replacement prior to any further use.
When it comes to wood stoves, they are designed to maintain excessive temperatures, however, the connections and pipe do not hold the same ability. A chimney fire can cause the wood stove pipe to buckle, warp, and completely separate from the wood stove allowing smoke and/or fire to escape into the home and onto surrounding combustible materials.
What Can I Do To Prevent A Chimney Fire?
The CSIA recommends, at minimum, having an annual inspection of your fireplace/firebox, flue system, and exterior. Cleaning can differ depending on how often you use your fireplace and the type of wood you are burning. The rule of thumb is approximately a face cord and a half of wood, but more often if the wood you are burning is not hard, dry, aged, or left in the elements. On average, this equates to approximately 50 or so fires.
Creosote logs, while they provide a bit of assistance with cleaning, do not replace chimney cleaning as a whole. You will still need chimney cleaning to remove the deposits from the chimney flue.