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Burning Out The Creosote

Q: My Dad used to "Burn Out" the creosote in our woodstove chimney every day. Reading through your Sweeps Library and other online chimney info sites, it seems the general consensus is that having a chimney fire is an event to be avoided, yet that is evidently what Dad was doing on a daily basis. Can it be that a series of small chimney fires is OK, so you don't ever have a big one? Or am I missing something here?

Sweepy The practice some people refer to as “burning out the chimney” doesn’t involve actual ignition of the creosote in the flue.

Every time you have a fire, some amount of liquid creosote condenses on the inside of your flue. The cooler the exhaust temperature, the more this condensation will occur, so the heaviest layers happen during all-night burns.

Two things cause liquid creosote to solidify: time, and temperature. If layer upon layer of wet creosote is allowed to build up over a series of long, low-temperature fires, it will eventually solidify over time, but often in the form we call glaze, which is extremely difficult to remove.

Here’s where temperature comes in. If you make it a practice to have a hot morning fire to send some heat up the flue after every all-night burn, the liquid creosote that has formed overnight will dry out quickly and solidify in easy-to-remove granular form, not glaze. This practice also helps cook the overnight creosote condensation off the viewing window.

The creosote that forms in the stovepipe overnight tends to be thinner than the layer that forms in the chimney, because the pipe is closer to the fire and stays hotter. The stovepipe gets super-hot during the morning fire, so the thin layer of creosote in the pipe will often dry out so quickly and thoroughly that it peels off in tiny shards like cornflakes, which fall back into the fire. This is often accompanied by a crackling sound in the pipe, and "sparkles" in the firebox where the flakes land and ignite. This might be where the phrase “burning off the creosote” originated.

       

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