Woodstoves, fireplaces, inserts and furnaces should be swept and inspected on a regular basis to avoid any incidence of chimney fire. Soot and creosote are by-products of incomplete combustion within the burning system. This can be caused by improper fuel loading, low burn habits, poor grade firewood or an improperly sized chimney flue. A low burning fire tends to make the combustion phase a smoldering production while a brisk hot fire makes for a great burning environment. To understand this you must begin to understand the basics of how wood burns.
How Wood Burns
When wood burns it goes through a chemical process called combustion. Combustion is easily explained by this formula.... Fuel + Heat + Air = Carbon Dioxide + Water Vapour + heat + Air. In a perfect world this is Complete Combustion, this rarely happens. What we generally get is an excess of hydrocarbons produced which form into soot, creosote and tarry substances. There are several different processes that happen with wood before the flames erupt.