Abstract The increasing diffusion of micro-cogeneration systems is raising the need for studying their environmental impact in order to assess their sustainability. The adoption of the systems for the combined production of heat and power may provide a significant reduction of global impact in terms of carbon dioxide emissions with respect to the separate production of electricity and heat. However, a comprehensive environmental evaluation of this technology should take into account as well the impact due to the presence of plants spread over the territory that could increase the local pollution, in particular due to nitrogen oxides and carbon monoxide, and thus could worsen the local air quality. In this paper the nitrogen oxides and carbon monoxide emissions of a residential building-integrated micro-cogeneration system were evaluated; a 6.0 kWel natural gas fuelled internal combustion engine-based micro-cogeneration unit was coupled with a multi-family house compliant with the transmittance values suggested by the Italian Law. The analyses were carried out by using the whole building simulation software TRNSYS upon varying the city where the building is located (four Italian cities representative of different climatic regions were considered) as well as the control logic of cogeneration device (electric and thermal load-following strategies). The simulated performance of the proposed system was compared with those of a conventional system composed of a natural gas-fired boiler (for thermal energy production) and a power plant mix connected to the central electric grid (for electricity production) in order to assess the suitability of the cogeneration-based system in reducing the local emissions.