If it's 1/8-in. thick, schedule a fireplace cleaning soon. If you have 1/4-in. of creosote or more, do not use the fireplace again until it is cleaned—a chimney fire could occur at any time.

While this is a nice secondary heat source, he has creosote buildup in the chimney to worry about. [Michel] knows that by carefully monitoring the temperature of the gases in the chimney ...