Soft woods, including pine and artificial logs, produce the highest level of creosote. These burn fast and leave a high deposit of creosote. Juniper is a little better. The best woods to use are hard woods, which include cedar, oak and mesquite. These burn slower, hotter and leave fewer deposits of creosote.
Creosote burns with an intense flame that can damage mortar.
In a matter of seconds the fire spreads up through the flue, as the creosote is burning, creating a draft that only helps the fire burn. The National Fire Protection Association recommends that chimneys be inspected once a year and cleaned if needed. When used regularly, the chimney should be checked every six months. You may be able to tell by using a powerful light and a mirror to look up the flue from the bottom. If the bricks look pink, you're okay.