District heating (DH) systems, together with combined heat and power (CHP) plants, have been increasing both in number and interest over the last decade, but the environmental improvements are still controversial, because although there is usually a reduction in CO2 emissions, a positive effect concerning other pollutants is not always certain. A limited number of works that pay particular attention to the local environmental effect due to DH plants have been found in a brief overview of DH papers. The energetic and environmental impact of a new DH+CHP plant has been investigated in the present paper, where this plant has been proposed to substitute the existing heating systems. The environmental aspects concerning the local variations due to some pollutants, such as sulfur oxides (SO.), particulate matter (PM) and nitrogen oxides (NO.), are in particular taken into account. The main data necessary for the analysis and the hypotheses that are useful to simulate the behavior of the local heating plant and DH plants (e.g. efficiency, the heating demand, etc.) are discussed. A dispersion model (Gaussian model) has been used to evaluate the effect at a local scale. Finally, a case study concerning a new DH+CHP plant in Northern Italy is presented and discussed. (C) 2008 Elsevier Ltd. All rights reserved.