Wood burning fireplaces, stoves, and space heaters may be a potential source of air pollution in the home. Combustion gases such as carbon monoxide and nitrogen dioxide, as well as particles released when fuels are incompletely burned can lead to lung irritation other health hazards. To avoid the accumulation of irritants, ensure damper, fireplace doors or both are closed when the unit is not in use, especially if an exterior chimney exists. Have fireplace flues and vent piping cleaned regularly. In addition, avoid burning wood that is not dry and is green.