This paper discusses the problem of fireside deposition observed during industrial gasification of feathers in a 3.5 MWth updraft fixed-bed plant equipped with steam boiler. The research included calculating mass balance of the system and performing an analysis of samples of bottom ash and fireside deposits collected from the plant, including XRF, XRD and melting characteristics. Analysis revealed that the bottom ashes and the fireside deposits, collected from the gasification and combustion chambers, consisted of hydroxyapatite with addition of silica and aluminium compounds, while the deposits collected from the boiler and the economiser were formed out of alkali and alkali earth metal sulphates, present in a form of eutectic systems such as 50CaSO(4)-30K(2)SO(4)-20Na(2)SO(4) and 30K(2)SO(4)-40Na(2)SO(4)-30ZnSO(4). The method of minimising fireside deposition by means of additives was discussed and alternative types of boilers suitable for feather gasification systems were proposed as a result of the study. (C) 2015 Elsevier B.V. All rights reserved.