The influence of process conditions on the overall heat demand during the pyrolysis of biomass was investigated. The results show that increasing the vapour residence time by an increasing initial sample weight or an increasing operating pressure results in an increasing char yield and in a decreasing heat demand. Lumped reaction schemes were used for data interpretation. They suggest that only an exothermic char formation process may justify the experimental results obtained. Influence of pressure, residence time and initial sample mass on biomass heat demand were correlated to the final char yield, confirming that the formation of char during pyrolysis is an exothermic process, independently of operating conditions. (C) 2016 Elsevier B.V. All rights reserved.