Biomass combustion for domestic heating can contribute to air pollution in residential areas with regard to ultrafine-particle concentrations. Measurements of ultrafine-particle concentrations were performed in a residential area with a diffusion-charge-based device during winter. In the morning and evening hours the concentration increases to, on average, twice the background level. The good-practice statement of a maximum 1 h mean of the World Health Organization is exceeded during 33.6 % of days.