The increase of renewable energy by combustion of biofuel will likely lead to an increase in the use of biofuels with high ash content. These fuels are more demanding from a combustion perspective. To facilitate combustion of these fuels in small combustion devices (50 kW – a few MW), there is a need of inexpensive dust cleaning devices. This is urgent to facilitate increased biofuel combustion without counteraction with the Swedish environmental goal Clean Air (which contain goals for particles in the air). Electrostatic filters for dust cleaning at heat and power plants are well established. However, the cost of these filters is often expensive to bear for a small plant. A few electrostatic filters for residential applications are available, but the experience is limited. In the capacity-area in between, i.e. small district heating plants, it is of special importance to find new cheap alternatives for an improved dust cleaning. The Norwegian company Applied Plasma Physics (APP) have products for dust- and odour-cleaning. APP also has the electrostatic filter called R_ESP (Residential Electrostatic Precipitator) for combustion of wood close to commercially available. The purpose of this report is to evaluate the electrostatic filter R_ESP at combustion of biofuels rich in ash, and by this contribute to increased knowledge about electrostatic precipitation at small-scale applications. A sub-goal is to separate 85 % of the particles in the flue gas. Experimental tests were performed at SP’s Energy laboratory. R_ESP was mounted downstream of a chimney, which was mounted on a multi-stoker/boiler. The multi-stoker has a nominal heat output of 65 kW at combustion of wood pellets. In this project pellets of bark or reed canary grass were fired. Dust separation efficiency over the R_ESP with respect to number concentration and size distribution was tested for several powers of the filter, during combustion of the two fuels. Combustion of bark was selected for a longer time test with respect to separation efficiency by particle mass. Number concentration and size distribution were measured in real time using an electrical low pressure impactor (ELPI) and mass concentration was measured by filter sampling. The combustion conditions were favourable, with low concentrations of hydrocarbons and carbon monoxide. The number concentration of particles was 2.5 · 107 #/cmN3 and 1.9 · #/cmN3 (normalised to 10 % O2) at combustion of reed canary grass and bark respectively. The results show that the technique of R_ESP works well for cleaning of particles from efficient combustion of the ash-rich fuels reed canary grass and bark. The combustion device was run at 20 kW, which is a thermal output that may be present at a farm or a school. For such an application the existing R_ESP may be tested in field, but for larger plants a certain product development is needed. The objective to separate 85 % of the particles was reached at normal operation of the filter (60 W). Lowering the effect of the filter, a large part of the dust separation is maintained and at 20 W the separation was about 80 %. At combustion of bark a two-day test of dust separation with respect to mass was performed. It showed on a dust separation efficiency of 82 % at 30 W power of the electrostatic filter.