We recommend that you have a licensed chimney contractor service your active fireplace(s) annually. When you burn wood or fossil fuels, your goal is to burn them as completely as possible. However, if the airflow to your fire isn’t adequate, it essentially starves the fire – leading to incomplete combustion. When the oils in the wood aren’t completely burned, they off-gas as volatiles and travel up through the smoke. The smoke cools as it rises, and ultimately condenses with water and other chemicals on the interior of your chimney and flue. This residue is called creosote. Creosote is not just a fire hazard but also an indoor air quality problem as this is a highly toxic substance that has been linked to cancer.