These can throw sparks out the chimney and can potentially ignite the roof. It has a tarlike consistency that clings to the linings of chimneys, Smith said. A buildup of creosote can ignite a chimney fire. However, chimney fires aren't always big, roaring balls of flame that scale up a flue in a matter of seconds. These flash fires can occur every 10 minutes without a homeowner knowing.
Liners also can crack due to bricks and mortar being installed too close to the liner.
Smith said he sees many examples of this especially in Janesville. Just because a home might not have a wood stove or fireplace, that doesn't mean the chimney can be ignored. Many homes' gas furnaces and other appliances vent through the chimney. If birds or other animals build nests in the chimney or if leaves or other material block it, carbon monoxide can pour right back into a home. It can lead to serious problems such as loss of consciousness, brain damage, muscle weakness, miscarriage and death.