Chimney Fire Advice
Your chimney–and the flue that lines it–adds architectural interest to your home, but its’ real function is to carry dangerous flue gases from your fireplace, wood stove or furnace safely out of your home.
As you relax in front of your fireplace or bask in the warmth of your wood stove, the last thing you are likely to be thinking about is the condition of your chimney. However, if you don’t give some thought to it before you light those winter fires, your enjoyment may be very short-lived.
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Why?
Dirty chimneys can cause chimney fires, which damage structures and can destroy homes. ​
Indications of a chimney fire have been described as creating:
loud cracking and popping noise (even where no cracking can be heard it is possible for damage to have occurred).
a lot of dense smoke, and
an intense, hot smell
​Chimney fires can burn explosively – noisy and dramatic enough to be detected by neighbours or people passing by. Flames or dense smoke may shoot from the top of the chimney. Homeowners report being startled by a low rumbling sound that reminds them of a freight train or a low flying airplane. However, those are only the chimney fires you know about.
The best way to prevent a chimney fire is to have an annual inspection performed by a OFTEC or Sweep Safe Certified Chimney Sweep.
Creosote is a black or brown residue that can be crusty and flaky…tar-like, drippy and sticky…or shiny and hardened. All forms are highly combustible. If it builds up in sufficient quantities – and the internal flue temperature is high enough – the result could be a chimney fire.
Conditions that encourage the buildup of creosote and chimney fires:
Restricted air supply (no ventilation/wall vent or not incorrectly sized vents or competition for air supply).
Unseasoned wood or wet turf/peat.
Cooler than normal chimney temperatures (uninsulated chimney, chimneys with an external wall, etc).
Air supply may be restricted by closing the glass doors, by failing to open the damper wide enough, and the lack of sufficient make-up air 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 the stove damper or air inlets too soon or too much. 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, then if seasoned wood is used. In the case of wood stoves, overloading the firebox with wood to get a longer burn time also contributes to creosote buildup.
The Effect of a Chimney Fire on Your Chimney
Masonry Chimneys
When a chimney fire occurs in a masonry chimney – whether the flue is an older, unlined type or tile lined to meet current safety codes – the high temperatures at which they burn (around 2000°F) can “melt mortar, crack tiles, cause liners to collapse and damage the outer masonry material”. Most often, thermal shock occurs and tiles crack and mortar is displaced, which provides a pathway for flames to reach the combustible wood frame of the house. This event is extremely dangerous, call 999 immediately.
Nine Signs that You’ve Had a Chimney Fire
Since a chimney, damaged by a chimney fire, can endanger a home and its’ occupants and a chimney fire can occur without anyone being aware of them it’s important to have your chimney regularly inspected by a Sweep Safe Certified Chimney Sweep. Here are the signs that a professional chimney sweep looks for:
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“Puffy” or “honey combed” creosote.
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Warped metal of the damper, metal smoke chamber connector pipe or factory-built metal chimney.
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Cracked or collapsed flue tiles, or tiles with large chunks missing.
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Discoloured and/or distorted rain cap.
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Heat-damaged TV antenna attached to the chimney.
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Creosote flakes and pieces found on the roof or ground.
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Roofing material damaged from hot creosote.
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Cracks in exterior masonry
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Evidence of smoke escaping through mortar joints of masonry or tile liners​.
If you think a chimney fire has occurred, call a Sweep Safe Certified Chimney Sweep for a professional evaluation. If your suspicions are confirmed, a certified sweep will be able to make recommendations about how to bring the system back into compliance with safety standards. Depending on the situation, you might need a few flue tiles replaced, a new liner system installed, or an entire chimney rebuilt. Each situation is unique and will dictate its own solution.
Proper Maintenance
Clean chimneys don’t catch fire. Make sure a OFTEC Registered/ SweepSafe Certified sweep inspects your solid fuel venting system annually and cleans and repairs it whenever needed. Your sweep may have other maintenance recommendations depending on how you use your fireplace or stove.