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3 Dangers That Can Damage Chimneys and Cause Fires

A well-built chimney stands tall and sturdy, appearing nearly impervious to the external elements while homeowners enjoy the warmth of a crackling fire in the fireplace. However, appearances can be deceiving. Just like any other structure, chimneys are not immune to wear and tear and other damaging effects. There are also three dangers that can ruin a chimney and cause a fire. 

Fishkill NY Chimney SweepingCreosote Build-Up

The primary cause of chimney fires and damage is excessive creosote build-up in the flue. Creosote is a naturally occurring carbon material that forms while burning fossil fuels and liquid fuels, such as wood and gas.  It begins as a benign white powdery substance that clings to the interior masonry walls, flue liner, and components. Unless it is removed, it will continue to accumulate, eventually maturing into a dark, crusty, and charcoal-like material that is highly flammable. It is also challenging to remove without professional assistance.

A chimney fire occurs when the sparks from a hot ember or the high temperatures in the fireplace ignite the creosote.

Many homeowners don’t realize they had a chimney fire until an inspection reveals fire-related damage. However, it’s a different story if the fire gets hot enough or if there was previous fire damage. The excessive heat in a chimney fire can cause flue tiles to crack or burst allowing the flames to spread throughout the entire house.  

According to the U.S. Consumer Product Safety Commission, chimney fires cause over $6B in property damage every year. Regular chimney cleaning is the best way to prevent a chimney fire.

Moisture Intrusion

Water intrusion is also dangerous for chimneys.  Moisture seeping inside the flue can lead to masonry damage that can increase the risk of fire and exposure to carbon monoxide fumes. There are several spots where a water leak can occur. One area, in particular, is through a cracked chimney crown. The chimney crown is a cement surface that is sloped to divert water from the chimney. When it cracks, water intrusion can occur and damage the interior masonry walls surrounding the flue. Another common place where water leaks occur is flashing. The flashing is a piece of metal that seals the seams where the chimney meets the roof. When the flashing is damaged or deteriorates, water can leak in the chimney, causing water stains on the ceiling or walls around the fireplace.  The damper is another area of concern. When the damper no longer forms an airtight seal, water can leak inside and cause the masonry and other components to deteriorate. 

Deteriorated Chimney BricksMasonry Damage

Another problem that can ruin a chimney is masonry damage. Normal wear and tear, settling, and earthquakes can damage masonry, but the most prevalent danger is the freeze-thaw effect. Although bricks and mortar are durable building materials, they are porous. In the winter, water-soaked bricks turn to ice when temperatures fall below freezing, causing the expansion of surface cracks in the bricks.


When the ice thaws during the day, moisture from the next rain or snow event fills in the broader cracks causing them to expand even further when it freezes again at night. The freeze-thaw effect can repeat daily throughout an entire season. When the damage is severe, it will cause bricks to spall where they fall off the chimney. The rain and snow can also erode the mortar leaving gaps in the joints that hold the bricks together. The freeze-thaw effect can also increase the risk of fire and be devastating to the structural integrity of the chimney. The chimney may lean or even collapse.

Annual chimney inspections and cleanings can help prevent chimney damage and fires. Contact your local chimney professional to schedule your annual chimney inspection today.

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