Signs of a Chimney Fire

September 12, 2014 in Signs of a Chimney Fire

melted cap

If you have just purchased a home, the inspection report should include details about the chimney’s past including any fires that might have happened.  Not every chimney fire will leave the same set of signs and effects, but because a fire creates conditions so dramatically different from those of a normal heating operation it is likely that every fire will cause changes in the physical state of both the creosote deposits and the chimney itself. When looking at your chimney, here are signs that it suffered a fire outbreak in the past:

 

  1. The chimney cap is distorted or looks burned or warped such as the one in the photo.
  2. The damper is warped or the metal handle of the damper is warped.
  3. There is foamy creosote buildup that expanded and is coating the liner and firebox.  It will have bubbles in it from where the burning occurred, and sometimes it will appear to have colors rather than be just plain black.
  4. The presence of non-uniformity in the flue is one of the more distinctive signs of a chimney fire.  This means the flue has tiles that are partially broken or crumbled and smoke stained.  Or, there is thick creosote bubbling on one side of the flue compared to the other.
  5. You may see chunks of creosote on your roof or falling into your fireplace.
  6. You see damage on the exterior of your house.  The roof or chimney’s masonry looks damaged by heat or cracked.  If there is evidence of smoke stains around the cracks, there was definitely a fire.

The conditions needed for ignition of a chimney fire are essentially the same as those necessary to start any fire:  adequate fuel, heat, and oxygen. Chimney fires are ignited when these elements come together unbeknownst to the homeowner.  A fire is avoided when one or more is deficient. The manner in which these factors are manifested accidently in a chimney is worth examining to help with future prevention.

Structural issues or cracks in your chimney liner allow high temperatures and embers to find their way into combustible areas in walls, the roof, or attics and start a fire. Chimney fires also occur when creosote, the by-product of burning wood, catches on fire inside of the chimney.  This is because creosote is highly combustible and it can easily ignite.  Chimney fires caused by creosote are ignited by direct contact of flames issuing from the fireplace or appliance onto deposits of creosote, or from non-burning flue gases that are hot enough to raise the creosote to its ignition temperature, or from sparks or embers carried from the fireplace that have settled on creosote deposits and started a fire.

Take some preventive steps to help avoid a chimney fire from starting in the first place.  Use the right firewood in your fireplace or wood-burning stove when you are burning wood, which means wood that has had about a year to dry out.  No freshly cut wood should be used because it is still retaining moisture that contributes to a lower temperature fire that creates more smoke and creosote.  Do not burn anything else in your fireplace such as trash, cardboard, paper, etc.  Make sure you have your damper open and an adequate draft when lighting a fire and keep everything sealed up when your fireplace or heating appliance is not in use. Most importantly, you need a professional chimney sweep to annually clean and inspect the inside of your chimney.  They will remove the buildup of creosote and check for any other hazards that could potentially cause a chimney fire.