The erosive wear of boiler tubes caused by fly ash in coal combustion flue gases has been studied for a long time. However, there are practically no data concerning the intensity of the erosion of the heating surfaces of boilers fired with both coal and biomass, and thus it is difficult to design these particular areas appropriately. The essential problem is the tendency of the fly ash from biomass combustion to produce ash deposits on the boiler convection surfaces and to cause slagging on the radiant surfaces. In such cases, both an increase in the deposits and a shortening of the time over which the ash fouling accumulates to the maximum level are observed. Consequently, if the boiler is fitted with steam or air blowers, they are started more frequently; if not, they have to be installed. The research conducted here proves that the situation leads to serious damage to the tubes, which results from the erosion caused by ash particles carried by the blowing agent jet. The authors of this paper attempt to make a quantitative evaluation of the impact of co-firing two types of biomass (coniferous wood chips and willow wood chips) on both types of tube erosion. (C) 2013 Elsevier Ltd. All rights reserved.