This paper presents an assessment of the energy, economic and greenhouse gas emissions performances of a WhisperGen Mk IV Stirling engine mu-CHP unit for use in a conventional house in the Republic of Ireland. The energy performance data used in this study was obtained from a field trial carried out in Belfast, Northern Ireland during the period June 2004-July 2005 by Northern Ireland Electricity and Phoenix Gas working in collaboration with Whispertech UK. A comparative performance analysis between the mu-CHP unit and a condensing gas boiler revealed that the mu-CHP unit resulted in an annual cost saving of (sic)180 with an incremental simple payback period of 13.8 years when compared to a condensing gas boiler. Electricity imported from the grid decreased by 20.8% while CO2 emissions decreased by 16.1%. The mu-CHP unit used 2889 kWh of gas more than the condensing gas boiler. (C) 2014 Elsevier Ltd. All rights reserved.