An effective-use method of exhaust heat for a fuel cell energy network (FEN), in which fuel cells installed in two or more buildings are connected, was considered. A program for planning the path for the hot-water piping network was developed in this study, and it can be used to plan the route which minimizes the amount of heat released in the piping considering the difference in temperature of the open air and hot water. In the plan of the hot-water piping network in the FEN, the energy demand pattern in each building and the electric power generation capacity of the fuel cell installed in each building confirmed the optimization of the hot-water piping path as a result of the analysis. Furthermore, when fluctuations in the electricity demand in each building linked to the FEN are large, the optimal path of hot-water piping differs from the case where there is no change in electricity demand. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.