To evaluate the environmental impact of massive heat-pump introduction on greenhouse gas (GHG) emissions, dynamic simulations of the overall electricity-generation system have been performed for Belgium. The simulations are carried out with Promix, a tool that models the overall electricity-generation system. For comparison, three heating devices are considered, namely conventional boilers, heat pumps and electrical resistance heating. The introduction of electric heating at the expense of classic heating increases the demand for electricity and generates a shift of emissions from fossil-fuel heating systems to electrical power plants. The replaced classic fossil-fuel-fired heating represents emissions of about 300 kton. With regard to the heat-pump scenarios, both direct heat-pump heating with a coefficient of performance (COP) of 2.5 and accumulation heat-pump heating with a COP of 5 are investigated. The results of the simulations reveal that the massive introduction of heat-pump heating is favourable to the environment. In Belgium, the largest reductions in GHG emissions occur with heat pumps for direct heating, combined with newly commissioned combined cycle (CC) gas-fired plants or with accumulation heat-pump heating. These scenarios bring about overall GHG emission reductions of approximately 200 kton compared with the reference case with conventional heating for the years 2000 and 2010. The amount of additional electricity-related emissions depends on the considered heating device. In 2010, the scenario with accumulation heat pumps results in an overall decrease of Belgian GHG emissions by 0.15% compared with the reference scenario. The expansion of the electricity-generation system with new CC plants has an important favourable impact on GHGs as well. In most cases, the combination of higher electricity demand and the construction of new gas-fired CC plants will lead to lower overall GHG emissions. Copyright (c) 2007 John Wiley & Sons, Ltd.