Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG Biomass is commonly used for heat production in small-scale and domestic facilities. Particulate matter (PM) emissions from the combustion of solid biomass are a concern because of hazards to human health. Electrostatic precipitators (ESPs) have been supported as the most promising mitigation technology, although there is a lack of consolidation to provide and promulgate a solution. The currently published studies on small-scale biomass do not offer a deep performance analysis of an electrostatic precipitator; instead, different designs have been presented and validated through efficiency measurements. In this work, an easily attachable ESP design is tested to more deeply analyse its performance with emissions from a pellet boiler, measuring its retention efficiency as a function of the PM sizes generated by the boiler, and under the influence of the supplied voltage and the geometry considering different discharge electrode diameters. Increasing voltage give higher separation efficiencies until 90% are reached, and further improvements are not remarkable. This efficiency value is influenced by the limitations of the particle analyser. A thinner discharge electrode achieves both better efficiencies and stable operation at lower voltage than a thicker electrode. Regarding the PM size, the retention capacity of the ESP is lower for particles between approximately 0.17 μm and 0.7 μm due to the reduced ability of the charging mechanisms. The formation of agglomerates during re-entrainment is also observed. Xunta de Galicia | Ref. ED481A-2019/225 Ministerio de Ciencia, Innovación y Universidades | Ref. RTI-2018-100765-B100