The results of a simulation of heat balance in the tube side of a heat exchanger operating in the superheated steam zone of a biomass combustion boiler are presented. The alkali salt deposits on the surface of the exchanger interfere with the heat transfer from hot gases to the superheated steam. A theoretical model has been used to assess the layer growth of these deposits depending on different operational parameters and to study the influence on the heat transfer rate. The weight of some variables such as the superheated steam temperature and pressure, the diameter of the heat exchanger tube or the particle diameter on the heat transfer losses is low (<1%) in the studied range. Other parameters, such as the hot gas temperature, concentration of alkali salts or gas speed, have a higher influence up to 4, 10 and 15%, respectively. (C) 2016 Elsevier Ltd. All rights reserved.