From two Albemarle County Fire Rescue Press Releases:
At 0839 hours on January 31, 2014, units responded to the report of a wall in flames inside a residence. The cause is classified as a chimney fire. The Fire Marshal’s office estimates the loss from this fire at $100,000.
At 0047 hrs on March 4, 2014, units responded to the report of a residential structure fire. The cause of the fire is a malfunctioning chimney. The Fire Marshal’s office estimates the loss for this fire at $130,000.
While the releases didn’t disclose whether these chimneys had been safety checked and properly cleaned, Assistant Albemarle County Fire Marshal Mel Bishop says, “During the winter months, half of all heating fires are in chimneys, stovepipes, and heating apparatus. Especially in rural areas, about 39 percent of winter fires are chimney fires.”
What does a chimney do?
Chimneys are necessary for any solid-fuel burning system such as a fireplace, woodstove, pellet stove, or coal stove. Non-electric furnaces also need venting which is sometimes combined in a chimney.
Chimneys carry the byproducts of combustion safely from the house. These byproducts can include smoke, unburned fuel particles, hydrocarbon, minerals, gases including carbon monoxide, and other substances.
Chimney fires can be frightening, sending flames and smoke pouring from the top of the chimney. They can also be slow burning when there is a meager supply of oxygen. “Sometimes a smoke alarm goes off,” says Bishop, “and homeowners finally discover fire in their attic from a chimney.”
In either case, high temperatures can cause damage to the chimney structure or even ignite the house. If you ever have a chimney fire, call 9-1-1 immediately!
While codes can vary from one region to another, in general they address the height of the chimney above the roof, the thickness of the chimney walls, the construction of the flue or chimney lining, and other safety requirements. In older construction, chimneys may be unlined and thus don’t meet current safety codes.
Factory-produced metal chimneys for venting woodstoves or metal fireplaces must generally withstand flue temperatures of over 2000 degrees Fahrenheit. However, the pipes connecting a woodstove to the flue may not withstand such temperatures and can warp or even separate in the event of a chimney fire.
When a chimney fire occurs, temperatures can exceed 2000 degrees, disintegrating mortar, cracking or collapsing tiles or liners, providing space for flames to ignite combustible materials of the house itself.
Why do chimney fires happen?
“The cause of chimney fires is the buildup of creosote,” explains Bishop, “often because of green wood.”
Creosote is all about those byproducts going up the chimney. It can be black or brown, flaky, sticky, crusty, or hardened to a dark gloss—sometimes all in the same chimney. In any case, it is highly combustible.
Creosote buildup can be fostered by burning unseasoned wood which uses a lot of its energy to vaporize the sap instead of producing heat. Another cause is a restricted air supply such as a partly open damper, glass doors on the fireplace being closed, or the fuel box being overloaded. These all result in a “cooler” fire with “cooler” smoke staying in the chimney longer, making creosote formation more likely.
“To make sure you don’t have a fire,” says Assistant Fire Marshal Bishop emphatically, “be sure you have a clean chimney.”
Both homeowners who choose the do-it-yourself route and professional sweeps use stiff wire brushes on an extendable rod to break creosote free, knocking it down into the fireplace or solid-fuel burning device. It can be a messy business. Stovepipes connecting to a chimney must be removed and reinstalled.
A professional chimney sweep should have the right tools as well as thorough training. “When you have a reputable sweep, the word will get around,” says Bishop. “A lot of times you can check with different businesses or people you know who have chimneys and have used a sweep.”
“Ask potential sweeps if they are certified,” suggests Jonathan Schnyer, co-owner of Wooden Sun in Charlottesville. “This requires an expensive and comprehensive course. The sweeps must follow best practices and continue classes to maintain credentials. There’s a lot more to sweeping than just a wire brush. A certified sweep can inspect for proper installation or chimney problems.”
The bottom line? You don’t get fires in a clean chimney.
In their previous house, Marilyn Pribus and her husband cleaned their chimney each fall before wood stove season began. Their Albemarle County home near Charlottesville, however, has a much higher chimney and they employ a sweep who arrives wearing a traditional top hat