Solid fuels boilers with low emission and modern construction, which are used for residential heating, require coal fuel with low sinterability (RI < 15). This paper presents a process for adapting coal with high sinterability for use in small boilers in residential heating systems. This solution allows for the combustion of coals with an RI of 50 without causing negative effects (in terms of combustion stability) in typical burners used in heating devices. The proposed solution involves the delivery of fuel particles coated with an oil film (waste oil and canola oil) to the combustion chamber. Tests were performed using a commercial-scale boiler with a 17-23 kW output, equipped with a retort burner and a dosing device, which applied oil to the coal in the boiler. Tests were performed during the combustion of hard coals characterized by different sinterability, with and without various streams of oils. Emission issues are also analysed. Impregnation of the coal by canola oil caused slightly lower NOx emissions, but higher CO and dust emissions. Analyses of the basic quality parameters (i.e., coal structure after thermal treatment) show that changes in the coal properties also occurred. Based on these studies, a mechanism that explains the beneficial effect of oil presence on high sinterable coal (HSC) combustion is proposed.