A dynamic numerical model describing an experimental methane fuel processor for a residential PEMFC energy system is presented. in contrast to previous simulation studies of steam reforming of methane, this model includes the various energetic couplings due to spatial proximity and constructive layout of the components. Thus, all significant energy flows inside the system are taken into account, including those caused by unintended conduction and radiation. Steady-state simulations were carried out to investigate the effect of a constructional modification in the reformer, which clearly reveal the significant influence of thermal couplings on the reformer efficiency. Furthermore, dynamic simulations were performed for the start-up procedure of the fuel processor and compared to experimental data. The results demonstrate that the dynamic model is a useful tool for further investigations of unsteady operating conditions and for optimisation with respect to both construction and system operation. (C) 2009 Elsevier Ltd. All rights reserved.