Without chimney cleaning, this idyllic scene would have the potential to cause a dangerous fire as the sparks encounter highly flammable creosote deposits on the chimney liner, or even nests that birds built in the chimney shaft. Cracks in the ceramic tiles of the chimney liner and missing mortar could allow lethal carbon monoxide to penetrate your home, causing immediate risk to your family's health. Without looking at the entire liner, there is no way to tell what is in your chimney or what condition your chimney liner is in.