The "skinny" on creosote and where it comes from
When a wood fire burns, it releases unburned gases. These unburned gases condensate on the walls of the chimney liner or flue tile and form a tarry or glazed substance called creosote. Creosote becomes dangerous when allowed to accumulate in the chimney where it becomes a fuel source for a potential chimney fire. Creosote build-up can be minimized by burning small hot fires and using dry, well seasoned wood, but the reality is the formation of creosote from burning wood cannot be avoided.
The dangers of creosote build-up
A chimney fire will occur when built-up creosote deposits are ignited by extreme heat from the fireplace. For this to occur, it requires that the creosote be subjected to high temperatures over 1,000 degrees or so.
Though 1,000+ degrees may seem a bit extreme, the following quote from the March 1990 Home & Hearth Magazine puts this all in good perspective. "Creosote build-up, by itself or in combination with other factors, was involved in 92% of chimney fires reported in a study commissioned by the Wood Heating Alliance. A build-up of as little as 1/8 to 1/4 inch of creosote is sufficient to create a fire hazard."
The first key to fireplace safety is cleaning
Eventually, every chimney requires a manual cleaning to remove creosote build-up. Since the formation of creosote is an unavoidable by-product of burning wood, cleaning your chimney becomes an unavoidable task as well. Cleaning a chimney on your own is a dirty job as well as being somewhat difficult to do. The proper brushes and techniques should be used to ensure that the sides of the chimney are swept clean of creosote buildup. More importantly, proper inspection should be done at every cleaning to ensure that there are no structural defects such as cracks or missing mortar joints in the chimney flue that could lead to eventual safety problems. For these reasons it is highly recommended that the task of cleaning be left to a CSIA Certified professional chimney sweep. The frequency for the cleanings can vary based on the amount of use that the fireplace receives but should never be longer than a year between cleanings.
"Chemical cleaning" is a great idea too
Understanding that creosote can begin to reform within a few days after cleaning, a regular method of ongoing maintenance is always recommended. To accomplish this, chemical cleaners are a great solution. Chemical cleaners, used during burning, will help to prevent creosote from reforming as well as helping to reduce chimney odors. These types of cleaners can be found in several different forms including powders, liquid sprays, logs and sticks. When selecting a product to use, keep in mind that the best alternative in chemical cleaners is one that can be used on a daily basis with every burn. My experience has been that the liquid sprays, such as Chimney RX Creosote Remover, are the best choice when selecting a cleaner. They tend to be the least expensive per application, they are extremely easy to use and, since they are used with every burn, they are the most effective at reducing ongoing creosote build-up.
Burning wood, whether in a fireplace or a wood burning appliance offers many advantages to the homeowner, including the lure of heating with wood and the joy of stoking the fireplace and tending to the demands of the fire. The energy savings that be gained by wood as an alternative fuel source have motivated many homeowners to become "wood burners". By taking a couple of steps to keep your fireplace clean from creosote build-up you will enjoy all of the benefits of natural wood without the risks of fire.