Abstract Mixtures of peat with bark and peat with straw were burned in a large lab-scale entrained flow reactor under controlled conditions, and deposits were collected on an air-cooled probe controlled at four to six different probe surface temperatures between 475 and 625 °C. The results show that the probe surface temperature has no effect on the deposition rate when peat is burned. When burning bark, either alone or in mixtures with peat, the deposition rate decreases with increasing probe surface temperature. When burning straw, either alone or in mixtures with peat, the deposition rate increases with increasing probe surface temperature up to 550 °C and remains constant at higher temperatures. The Cl content in the deposits decreases with increasing probe surface temperature, regardless of the mixture composition. In deposits obtained from burning peat–bark mixtures, K appears as K 2 SO 4 when the deposition rate is low and as KCl when the deposition rate is high. In deposits obtained from burning peat–straw mixtures, no clear relationship is found between the deposition rate and the contents of Cl, S and K in the deposits.