The aim of this paper is to provide general guidelines for the design of micro-CHP systems for the heating of residential buildings. A micro-CHP system is intended as a system composed of a prime mover, a thermal storage system and an auxiliary boiler. In particular, the analyses carried out in the paper provide guidelines to select the proper prime mover technology and size and thermal storage system size, with reference to prime mover operating hours and produced electric and thermal energy. Moreover, both primary energy saving and profitability of the CHP system compared to the separate production of electricity and heat are also evaluated. (C) 2011 Elsevier Ltd. All rights reserved.