Creosote and Chimney Fires: What You Must Know.

Fireplaces and wood stoves are designed to safely contain wood-fuel fires, while providing heat for a home. The chimneys that serve them have the job of expelling the by-products of combustion- the substances produced when wood burns. These include smoke, water vapour, gases, unburned wood particles, hydrocarbon volatile, tar fog and assorted minerals. As these substances exit the fireplace
or wood stove, and flow up into the relatively cooler chimney, condensation occurs. The resulting residue that sticks to the inner walls of the chimney is called creosote.

Creosote is black or brown in appearance. It can be crusty and flaky...tar-like, drippy and sticky..or shiny and hardened. Often, all forms will occur in one chimney system. Whatever form it takes, creosote is highly combustible. If it builds up in sufficient quantities-and catches fire inside the chimney flue instead of the firebox of the fireplace or wood stove- the result will be a chimney fire. Although any amount of creosote can burn, we at Chimney Solutions are concerned when creosote builds up in sufficient quantities to sustain a long, hot destructive fire.

Certain conditions encourage the buildup of creosote. Simply put, restricted air supply, unseasoned wood and cooler-than-normal chimney temperatures are all factors that can accelerate the buildup of creosote on chimney flue walls. Air supplies on fireplaces may be restricted by closed glass doors or by failure to open the damper wide enough to move heated smoke up the chimney rapidly (the longer the smoke's "residence time" in the flue, the more likely is it that creosote will form). A wood stove's air supply can be limited by closing down the stove damper or air inlets too soon and too much, and by improperly using the stovepipe damper to restrict air movement. Burning unseasoned wood- because so much energy is used initially just to drive off the water trapped in the cells of the logs- keeps the resulting smoke cooler, as it moves through the system, than if dried seasoned wood is used. In the case of wood stoves, fully packed loads of wood ( that give large cool fires and 8 or 10 hours burn times) also contribute to creosote buildup. Cool flue temperatures speed creosote production, too. Condensation of the unburned by-products of combustion occurs more rapidly in an exterior chimney, for example, than in a chimney that runs through the centre of a house and exposes only the upper reaches of the flue to the elements.

Masonry Chimneys. When chimney fires occur in masonry chimneys- whether the flues are an older, unlined type or are tile lined to meet current safety codes- the high temperatures at which they burn (around 2000 degrees F) can "melt mortar, crack tiles, cause liners to collapse and damage the outer masonry material" . Most often, tiles crack and mortar is displaced, which provides a pathway
for flames to reach the combustible woodframe of the house. One chimney fire may not harm a home.
A second can burn it down. 

Chimney fires can occur without anyone being aware of them. If you think a chimney fire has occurred, please call Patrick Cowan ( 0872574267 ) for a professional evaluation. If your suspicions are confirmed, we will be able to make recommendations about how to bring your system back into compliance with safety standards. Depending on the situation, you might need a few tiles replaced, a relining system installed
or an entire chimney rebuilt. Each situation is unique and will dictate its own solution.