Concentration of CO is the basic parameter (besides concentration of O2) for proper boiler operation. A good knowledge of concentration of carbon monoxide becomes, beside a knowledge of oxygen concentration, a deciding factor to carry out a proper combustion process. Changes in fuel parameters or changes in boiler load make oxygen analysis not sufficient for proper combustion optimization. The parameter which provide an optimum operation of the boiler (minimum chimney's losses and from incomplete combustion process - near stechiometric point) is appropriate concentration of carbon monoxide. Usually it ranges between 30 and 350 ppm CO. Analytics provides CO analyzers which are dedicated to make a precise measurement of carbon monoxide.