Exploding Chimneys: Causes And Prevention Measures

It's a few days before Christmas, and you light a nice, toasty fire to set the holiday mood. All of a sudden, you hear a boom, a thud, and lots of stuff hitting the roof. Is it Santa coming early? Has his rocket sled crashed into your roof? No, apparently from the outside view of your house, your chimney has exploded! Does that sound about right? Here are a few reasons why this happened and what you can do to prevent it from happening again.

Creosote Buildup

Creosote is the ashen residue that accumulates on fireplace and chimney walls. It can get very thick and create pockets of air inside its own accumulation. Once it is really thick and has plenty of these little pockets of air inside, it becomes a time bomb. A spark, a flame that rises just high enough—that is all it takes to make large blockages of creosote explode. When it goes, so does your chimney.

The creosote can be cleaned out by a professional chimney sweep, or by a roofer that knows how to do this job. Large, wiry brushes are shoved down the chimney and used to scrape the interior. The scrapings fall down the chimney and into the fireplace in a black, smoky, powdery mess, so make sure your furniture and the floor are covered before the sweeping gets under way. If you do this annually, or biannually if you do not light a lot of fires in the fireplace, your chimney will be safe.

You Forgot to Open the Flue

It is a common mistake. You close the flue to prevent squirrels and birds from getting into the house during warmer weather, and then forget to open the flue before starting the first fire in winter. The result is a lot of smoke and fire, and heat builds, looking for an exit. With the glass gates closed on the fireplace, the smoke fire and heat cannot escape that way, so the pressure builds until it creates an explosion.

The problem is that once it explodes, a fire begins because the resulting opening from the explosion takes on the back draft effect. At this point, you will need a bunch of firefighters to put out the fire. Then you will need a roof repair team if the holidays are going to happen at home at all. It could have been prevented if you had only checked the flue and opened it.


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