Wood from old buildings, demolition wood, has a considerable energy value and can be used as a fuel. However, the material contains impurities that may have harmful effects. This investigation, carried out in a fluidized-bed boiler, focuses on the formation of deposits on heat transfer surfaces during combustion of demolition wood. To avoid inhomogeneity and variations in composition of the fuel during the tests, high-quality wood was used and two substances that are suspected to contribute most to deposits, chlorine and zinc ( from paint), were added in predetermined quantities. It was found that chlorine was the most harmful constituent, promoting deposits in the form of potassium chloride and also zinc chloride. The deposits from wood combustion or from wood contaminated with zinc are deemed not to be excessively harmful with respect to corrosion as long as the chlorine concentration is low and oxidizing conditions prevail.