Residential Fuel Cell micro combined heat and power (FC-mu CHP) systems can help decarburizing the energy system. In the European ene.field project, the environmental performance of FC-mu CHP under different conditions was therefore evaluated by means of a comprehensive Life Cycle Assessment (LCA). Important influential factors were explored, i.e. heating demands, full load hours (FLHs) and electricity replacement mixes (ERMs). The systems were compared with a stand-alone Gas Condensing Boiler (GCB) and a heat pump (HP, only in single family homes, SFHs). For the initially assumed FLHs and the current ENTSO-E ERM, relevant environmental impacts including climate change are generally smaller for the FC-mu CHPs than for the HP and the stand-alone GCB. In the setting "existing SFHs in central climate" with the highest deployment potential, GHG emission savings are higher the more carbon-intensive the ERM is and/or higher the net electricity export into the grid is. The results are discussed and put into perspective. Further research demands as well as product development opportunities are outlined. The importance of a green hydrogen economy is emphasized. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.