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What is a chimney fire? Why is it A BAD THING?

Short Answer:  When creosote builds up in a chimney, it can ignite and burn.  That’s a chimney fire.  That fire can reach temperatures as high as 2000° F;  and it can wreak havoc on the insides (and sometimes the outside) of a chimney.  Resulting damage can lead to premature deterioration of the structure at best.  It can endanger a home and its occupants at worst.

We can find our substantiation for this opinion in The Facts about Chimney Fires – Causes & Cures — a brochure written by the Chimney Safety Institute of America.  Most of what is in this blog will be coming directly from that information piece. Some of it is directly quoted, some of it is paraphrased.

A chimney fire can be impressive.  Chimney fires have been described as creating:

  • loud cracking and popping noise
  • a lot of dense smoke, and
  • an intense, hot smell

The Dangers of A Chimney FireChimney fires can be  noisy and dramatic enough to be seen by neighbors or passers-by.  Flames or dense smoke may shoot from the top of the chimney.  Some report 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.  Slow-burning chimney fires don’t get enough air or have fuel to be dramatic or visible.  However the temperatures they reach are very high and can cause as much damage as their more spectacular cousins.“

So…what is creosote and how can you minimize its collection in your chimney?  Let’s consult  The Facts About Chimney Fires

“The by-products of combustion (smoke, water vapor, gases, unburned wood particles, hydrocarbon volatiles, tar fog and assorted minerals) exit through a chimney during the process of using a fireplace or wood stove.

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.   All forms can occur in one chimney system.  Whatever form it takes, creosote is highly combustible. If it builds up in sufficient quantities – and the internal flue temperature is high enough – the result could be a chimney fire.

Certain conditions encourage or accelerate the buildup of creosote on the chimney walls

  • Restricted air supply
  • closing the glass doors
  • failing to open the damper wide enough
  • the lack of sufficient make-up air  to move heated smoke up the chimney rapidly
  • closing down the stove damper or air inlets too soon or too much.
  • unseasoned wood
  • so much energy is used initially just to drive off the water trapped in the cells of the logs– keeps the resulting smoke cooler, than if seasoned wood is used.
  • cooler than normal chimney temperatures
  • exterior chimneys
  • uninsulated chimneys”


How do you know if you’ve had a chimney fire?  For answers, let’s go back to The Facts About Chimney Fires

We’ve learned that a chimney fire can occur without anyone being aware of it.  So….

”…it’s  important to have your chimney regularly inspected by a CSIA Certified Chimney Sweep.   Here are the signs that a professional chimney sweep looks for:

  • “Puffy” or “honey combed” creosote
  • Warped metal of the damper, metal smoke chamber connector pipe or factory-built metal chimney
  • Cracked or collapsed flue tiles, or tiles with large chunks missing
  • Discolored and/or distorted rain cap
  • Heat-damaged TV antenna attached to the chimney
  • Creosote flakes and pieces found on the roof or ground
  • Roofing material damaged from hot creosote
  • Cracks in exterior masonry
  • Evidence of smoke escaping through mortar joints of masonry or tile liners”


Blue Sky Chimney Sweeps |Bless Your Hearth can help you with….

Inspections & Proper Maintenance

“Clean chimneys don’t catch fire. Make sure a CSIA Certified Chimney 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.”

Visit to see the complete brochure:  The Facts about Chimney Fires – Causes & Cures

What do Chimney Fires and Termites have in common?

Both can cost you thousands of dollars if you don’t get an inspection!

What do chimney fires and termites have in common - Spartanburg SC - Bless your hearth

Everyone knows that it’s required to get a termite inspection by a reputable pest control company when a house is being sold.  Have you ever wondered why it’s not required to have the chimney/fireplace inspected by a certified chimney professional when that same house is being sold?  Well, unfortunately, I don’t have the answer for that here today.  However, after being in this industry for more than 36 years, I can give you my perspective on why it should be a requirement.

Bad things can happen to chimneys!

  • Chimneys can be built badly – so badly that they will not work well.
    • The flue may be too small or too large
    • The chimney may be too short.
    • The smoke chamber may be unparged, too tall or not tall enough.
    • Pre manufactured chimneys may not be put together properly and sometimes they are even installed with pieces and parts missing.
    • Flue liners may have been constructed with large gaps between them where they have not been mortared together properly.
  • Chimney fires can cause damage that can cost thousands of dollars to repair.
    • The National Fire Protection Association Standard 211 stipulates that ceramic chimney liners (terracotta flue tiles) that have cracks or gaps should be repaired or replaced before use.
    • Some manufacturers of prefabricated fireplaces even stipulate that manufactured chimneys that have sustained a chimney fire must be replaced.
  • Deterioration due to age, neglect and water intrusion can render a chimney unusable.
    • Many unlined chimneys in very old homes have collapsed wythes (the interior walls of the chimney that separates the different flues) effectively blocking the flue passage

These are just a few of the things our technicians find when we are called out to inspect chimneys for a house under contract.  Some of these defects are impossible to see without an internal scan of the chimney.  Therefore we follow the guidelines set out by the National Fire Protection Association in their published inspection standard (NFPA 211).  Their requirement is that a Level 2 inspection be performed where a house sale is involved.


Level 2 Inspections– A Level 2 inspection is required when any changes are made to the system. Changes can include a change in the fuel type, changes to the shape of, or material in, the flue (i.e. relining), or the replacement or addition of an appliance of a dissimilar type, input rating or efficiency. Additionally, a Level 2 inspection is required upon the sale or transfer of a property or after an operation malfunction or external event that is likely to have caused damage to the chimney. Building fires, chimney fires, seismic events as well as weather events are all indicators that this level of inspection is warranted….NFPA 211


Other “changes” requiring a Level 2 Inspection (per NFPA 211):

  • Fuel type –
    • gas to wood
    • wood to gas
  • Replacement of an appliance –
    • new upgraded wood stove
    • adding a wood stove or wood stove insert
  • Chimney fire occurrence


So…the bottom line in all this is — if you are buying a house and it has a (supposedly) functioning chimney, it is our opinion that it would be to your advantage to pay the extra for an NFPA 211 Level 2 Inspection by a CSIA Certified Chimney Sweep.  What you find out could protect you from disappointment or costly expense down the road.