An SOFC (Solid Oxide Fuel Cell) cogeneration optimization study was carried out for one small-scale and one large-scale building under both hot and cold weather conditions. Several different configurations of the SOFC system are operated using a defined set of input parameters to meet the actual heating, cooling and electrical demands on those two buildings The results are discussed and compared from four different perspectives: electric-only vs. cogeneration, energetic vs. economic, large-scale vs. small-scale buildings and hot vs. cold weather conditions. The main conclusion of this study is that optimization results vary widely depending on different system configurations and loading conditions and thus SOFC systems should be optimized based on the specific conditions to which they are exposed and not simply on a single operating condition. (C) 2009 Elsevier Ltd. All rights reserved.