The aim of the present work is to study the viability of a cofiring system in a small-scale biomass plant using a mixture of wood pellet and refuse derived fuel (RDF pellet). RDF comes from municipal solid waste, and a valorization process via combustion is a useful way of solving the problem of the accumulation of nonrecyclable wastes. In this paper, the characterization of both fuels is carried out. In addition, a new procedure for measuring emissions, based on artificial dilution, is presented, allowing for the measurement of high peaks of certain species, such as CO, forthcoming in the cofiring process. Improving the overall process is necessary to comply with EU rules on biomass emissions. Accordingly, two approaches are studied; the use of a secondary air supply and the recirculation of gases. The results obtained indicate a better performance, thereby allowing for the application of the process to a real system (nonexperimental one).