Company Blog

Chimney Fire Science

When wood is heated, burnable hydro-carbon gases are released. When the gases get hot enough and mix with air — there is fire. When the fire is not burned hot enough, the unburned gases condense and collect on the inside of stovepipes and flues as runny acids and liquid tars that harden into creosote. Creosote is flammable. If what’s in the chimney ignites – there is a chimney fire!

What contributes to a fire that is not hot enough? –a fire that encourages condensation? –a fire that makes creosote?

A cool fire :

A flue that is too big for the appliance it serves

Poor woodburning habits:

• Severely limiting the air supply in a stove to achieve a long burn causes a sluggish draft and a smoldering fire that doesn’t get hot enough to burn the hydro-carbon gases.

An oversized or out dated stove:

• A stove that is too big for the space it heats, is likely to be burned in a closed down, creosote-producing way
  Steam from green or wet wood – remember the heating up part we talked about above? Well, green or wet wood has to dry out before it can heat up enough to release the gases that can burn. As it heats it releases steam that lowers the flue temperatures. Lower flue temperatures cause the other hydro-carbon gases already in the flue to cool and condense on the sides of the flue.

What does creosote look like?

It has various forms.

• Sooty powder
• Crisp and crunchy
• Gummy drippy mess
• Hard glaze
• Burnt marshmellows

Is there any way NOT to make creosote?

…or at least minimize how much is made? Yes!

• Install an insulated flue liner that is properly sized for the appliance you are using (i.e. fireplace, wood stove insert, free standing heater).
• Burn smaller hotter fires. (use seasoned wood or a mix of seasoned and green wood)
• Replace an old stove with a new unit correctly sized for the space you are heating.

So what if you already have a creosote problem?

Find an experienced CSIA Certified Chimney Sweep right away. Put your fireplace or wood stove system on a regular inspection and maintenance schedule.

Chimney fires can burn like a blast furnace and sound like a freight train and look like a fireworks display. Sparks or burning embers from the fire can put your roof and home at risk. Chimney fires can also smolder silently so hot and for so long that it eventually catches wooden structure close to it afire simply from heat transfer. A chimney fire is definitely on the short list of things to be avoided. If you think you have experienced a chimney fire, call us for a free copy of the Chimney Safety Institute of America’s public service brochure entitled What You Need to Know After a Chimney Fire!

Keeping fire in its place in your home is a priority for Blue Sky Chimney Sweeps | Bless Your Hearth. Call today (864-682-5422) to schedule your chimney inspection and sweep service.

Creosote F.A.Q.

One of the leading causes of chimney fires, according to the Chimney Safety Institute of America (CSIA), creosote build-up is a dangerous fact of life when you have a wood-burning fireplace or stove. Removing creosote deposits from your chimney walls is a big part of your annual chimney sweeping, and this maintenance can save you and your family’s life since creosote building up on your chimney walls puts you at risk of a chimney fire.

It isn’t possible to clean 100% of the creosote in your chimney. However, you need regular maintenance to keep the level low.

The CSIA-certified chimney sweeps at Blue Sky Chimney Sweeps clean your chimney thoroughly to remove any creosote sticking to your chimney walls when performing their chimney sweeps. We at Blue Sky Chimney Sweeps would like to answer some of the most frequently asked questions we receive about creosote to inform you about this fire hazard.

What exactly is creosote and how does it get in my chimney?  Occurring naturally, creosote is the resulting residue of the condensation that occurs when the by-products of combustion (smoke, gases, vapors, unburned wood particles, tar fog, and other assorted minerals) leave the fireplace or wood stove and exit the cooler upper chimney. This residue sticks behind on the chimney walls.

What does creosote look like? Varying in appearance, creosote can be either black or brown, and it takes different forms: sticky and tar-like, flat and shiny, and crusty and flaky. No matter what it looks like, creosote is highly combustible in every form.

How does creosote build-up start chimney fires? If the build-up is large enough and your internal chimney flue temperature gets hot enough, a chimney fire could ignite, thanks to the highly combustible makeup of creosote.

Are there conditions that encourage the development of creosote deposits? Yes, certain things to help creosote to build up more quickly: restricted air flow, burning unseasoned wood, and cooler than normal chimney temperatures.

What can I do to change these conditions? To keep air flowing properly and without restrictions, open the glass fireplace doors when burning a fire, and always be sure your damper is wide open when burning a fire. You want to be sure you have enough air flowing into your fireplace to move heated smoke up the chimney quickly because the longer the smoke stays in the flue, the more likely creosote will form. When using a wood stove, do not close down the stove damper or air inlets too soon or too much. Always use seasoned firewood because burning unseasoned wood keeps the smoke cooler because the fire spends so much time burning off the excess water in the wood cells. Also, when using a wood stove, never overload the firebox with wood in an attempt to get a longer burn time because this also adds to creosote development.

What is the best way to prevent the accumulation of large creosote deposits? As the CSIA says, “clean chimneys don’t catch fire.” Having your chimney swept annually by a CSIA-certified company like Blue Sky Chimney Sweeps is the best possible prevention of creosote building up large enough to ignite a chimney fire. Our chimney sweeps are well experienced with creosote removal, and can rid your chimney walls of all creosote deposits.

If you have more questions about creosote and chimney fires, contact Blue Sky Chimney Sweeps today. We will be happy to schedule an appointment for your annual chimney cleaning to give yourself peace of mind regarding a possible chimney fire.