Chimney fires in chimneys serving wood-burning stoves, fireplace inserts, fireplaces and furnaces occur because of a lack of regular cleaning to remove creosote, which is the residue left behind by unburned fuel. The National Fire Protection Association recommends annual inspection and cleaning as necessary by a professional chimney sweep.
If a chimney fire occurs, close the damper and doors if possible, get out of the house, and call the fire department. Do not use the chimney until it has been inspected by a CSIA Certified Chimney Sweep. Firemen and home inspectors are not trained in evaluating chimney damages, but professional chimney sweeps are trained in this area. Homeowners can tell if a chimney fire is occurring if they hear a loud roaring or freight-train like sound or see flames or sparks coming from the exterior of the chimney at the top or sides, if chimney pipe turns red, or if the appliance suddenly stops drafting. However, most chimney fires occur without the homeowner’s knowledge while they are out of the room. Fire damage such as cracked flue liners and blown out mortar joints are usually found during a routine annual inspection by a professional chimney sweep, and these issues make the chimney a potential hazard.
Creosote comes in four forms: Stage 1 is a light dusty coating that comes off easily with brushes, State 2 is a harder and larger, but still comes off with heavy brushing, Stage 3 creosote is also known as glazed, baked-on or tar glaze creosote, which is the most flammable type. Glazed creosote will not come off by brushing. Glazed creosote bakes on the flue walls and can only be removed by power cleaning with chains or wire brushes on a drill. Removal of this type of creosote is a difficult, time-consuming, and dangerous process, so the best thing to do is avoid the accumulation of glazed creosote altogether by using proper wood-burning habits and having the right chimney or flue for the appliance. The fourth type of creosote is burnt glazed creosote, which occurs when glazed creosote catches fire and expands to ten times its original size. It has a honeycomb appearance and is very lightweight. Sometimes burnt creosote expands inside the flue, completely or partially choking off draft. This is why sudden smoking of an appliance is an indication of a chimney fire.
Always make sure the correct size flue liner or chimney is being used for the appliance. Open fireplace require large flues, wood-burning inserts require very small stainless steel flue liners, and freestanding stoves need small stainless steel chimneys, or if connected to a masonry chimney, a small steel flue liner. The manufacturer of the stove will have information about the best flue size to use. Never install a wood-burning stove insert into a fireplace without a stainless steel flue liner. A steel flue liner is required by code and by all manufacturers of wood-burning appliances.
Tips for safe wood-burning:
- Don’t burn treated wood, railroad ties, trash, or colored paper since they emit toxic fumes.
- Don’t burn pine trees or railroad ties since they create excessive amounts of flammable creosote and may overheat and warp a steel or cast iron appliance.
- Burning Hedge is also discouraged since it burns very hot and can overheat a woodstove or fireplace. In a pinch, use only one Hedge log to every two Oak logs.The best wood to burn is oak because it is very dense and burns slowly. However, any dry hardwood or soft wood may be used.
- Burn a wood stove hot (400-700 degrees) to assure complete combustion, which is how the stove is designed to be used, and it is cleaner and better for the environment. After establishing the fire, there should be white or clear smoke coming out of the chimney. If the smoke is grey or black, something is wrong with the wood, your burning methods, or with the chimney system. Stove thermometers are available from stove retailers and chimney sweeps.
- Have the chimney checked annually or every two months during the heating season if used for the primary source of heat, and cleaned as necessary by a professional CSIA Certified Chimney Sweep.
- Follow operating instructions by the manufacturer (if applicable) to assure safe and efficient heating.
- Keep combustible materials (including furniture) at least 3’ away from the front of the appliance.
- A screen should be placed in front of open fireplaces to keep embers and sparks from popping out. This is required by code.
- Place a child guard screen around stoves to keep children from getting burned.
- Never use flammable liquids to start a fire—the fumes can ignite and explode. Use an approved gel, fatwood, or firestarter.
- Remove flammable materials such as stockings from the mantel before starting a fire.
- Use a metal container to transport ashes to the exterior of the home. Ashes can smolder for days and cause nearby combustibles to ignite.
- Do not build large fires or long-burning fires in open fireplaces. Fireplaces are designed for small, ambient fires only, and are not heating devices. They are listed as “Decorative Appliances.” If you want to make your masonry fireplace energy efficient and a heating source, have a wood or gas fireplace insert installed by a professional.
- Have a heavy duty stainless steel chimney cover installed to keep damaging rain, animals, and debris out of the chimney. Beware of cheap black steel covers that rust badly.