The safety guidelines set by the National Fire Protection Association call for annual professional inspections of all wood and coal stoves, fireplaces, chimneys, chimney connectors, and all other solid-fueled heating equipment. Follow up cleaning should be done according to inspection results.
Why chimneys get dirty
Creosote and soot are natural byproducts of burning fuel, deposited on the inside of your chimney or flue pipe as a solid sticky, black layer that is highly flammable. This needs to be regularly cleaned from your chimney or flue pipe. To reduce build up and use fuel efficiently, keep your fires hot, and provide them with plenty of oxygen. Damping fires to keep them burning longer produces more smoke and solid by-products. On average, your chimney needs to be cleaned after every two cords of wood that are burned.
How the chimney is cleaned
Brushes are used to remove creosote and soot from the firebox, smoke shelf, elbows, and connector pipes. This is done from both outside and inside the house. Occasionally there is creosote buildup that cannot be removed by brushing. Professional chimney sweeps use chemicals to alter the composition of the hardened creosote and turn it into a powdery substance that can be easily removed.
Chemical vs. mechanical cleaning
Chemical chimney cleaning products are available for use by homeowners. The Chimney Safety Institute of America (CSIA) cautions against using these products to replace professional, mechanical cleaning of the chimney. Homeowners should be aware that these products can loosen debris that can fall into hard to reach places in the chimney structure and cause malfunctioning of the chimney. In addition, professional inspection is important because it often reveals hidden problems with the structure of a chimney that would otherwise go unnoticed, and could be potentially hazardous.
Chimney sweeps can receive national certification through the Chimney Safety Institute of America. In addition, they can be certified at the state level.