WOOD BURNING Guidelines - Reducing Creosote

By Shari Blank

Note: The newer EPA-Approved wood stoves produce MUCH less creosote than the older (pre-1988) models. However, any stove used improperly can produce excess tars and creosote.

Creosote is the product of wood smoke and moisture. It can be a serious hazard for homeowners who burn wood. Creosote is formed by burning wood which is unseasoned or burning at a low temperature. Several types of magnetic thermometer are available and can be used on the stove top to indicate a safe burn rate to help eliminate creosote build up. These magnetic thermometers start in price at about $10.00. The formation of creosote can be a nuisance because it may drip out of stove pipe joints which have not been properly sealed or installed; leaving a gummy stain and a acrid smell possibly ruining wall finishes or flooring.

A chimney fire occurs when a creosote buildup ignites and burns inside the chimney and stove pipes. A loud whooshing noise or glowing stivepipe are possible indication of a chimney fire. There are several types of chimney fire extinguishers available, and one should always be kept on hand for this type of emergency. The cost is very inexpensive compared to the possible consequences.

Chimney fires resulting from creosote burn at temperatures near 2,000 degrees, hot enough to damage some metal chimneys. These chimney fires can be very difficult to put out and preventative measures should be taken before this tragedy occurs.

Wet or unseasoned wood greatly increases the accumulation of creosote. The large amount of moisture from burning wet wood condenses in the chimney and adds to creosote formation as well as the acrid odor. The periodic use of a good liquid or powder chimney cleaner which is sprayed on the burning wood is essential to the wood burner. This type of product will not elminiate the need to clean your chimney or the formation of creosote, but it will make the cleaning task much easier.

Cool chimney pipes and masonry chimneys cause condensation rather than complete burning of wood gases above a fire. This moisture is formed on the inside walls of the chimney as creosote. Insulated metal chimneys, with most of their length outside the house, may be a slight bit cooler than those installed with the insulated pipe running straight up. This would also mean that your chimney may take a bit longer to reverse the downdraft before starting the fire. The straight up type installation gets the benefit of the warmth from inside your home.

The type of wood you burn is not as important a factor in wood burning as the creosote formation from improper burning technique (see Starting a fire and Tending a Fire). There is not much difference between creosote forming from burning dry softwood as compared to burning green hardwoods. Hardwood, if unseasoned or wet, could even produce more creosote than pine.

The following are just a few suggestions for reducing creosote buildup and getting the most out of your wood burning.

Season wood for at least six months - Store under cover. Hardwoods are preferred.

Do not use an oversized stove. Keeping a small fire at a low burn will cause creosote buildup.

Keep as much chimney as possible inside the house. Chimneys outside cool quickly (and are much harder to warm) causing creosote to build on cooler surfaces.

Stove pipe joints should be made with crimped end of your pipe facing down toward the stove. The pipe that sits directly on top of the stove should always go into the flue collar and not around the exterior. This will allow any creosote drippings to be inside the stove, and not on your floor or walls. Using sheet metal screws and also spreading around the two joined pipe a high temperature furnace cement. The screws will prevent the stove pipe from separating due to heat etc., and the furnace cement will keep smoke or creosote from leaking from the joints

If a chimney fire does occur, immediately shut off the air supply by closing all dampers and air openings on the stove or glass doors of the fireplace. If the fire in the stove or fireplace can be extinguished safely, put it out as quickly and safely as possible. Flare type chimney fire extinguishers, called Chimfex, are avaiable at your local hearth shop. A dry chemical fire extinguisher also works well in putting out a wood fire. Never throw water on a stove fire as it could cause a large burst of steam and also possible burns. When working around a wood stove or fireplace a good pair of fireproof gloves are a must.

Cleaning chimneys, whether masonry or insulated pipe, at least once per year can decrease the formation of creosote and the hazards caused by the buildup.

Building a hot roaring fire for a few minutes after each load of fire wood will go a long way in preventing the formation of creosote.

Keeping your chimney clean will pay off in increased safety and efficiency.