Two species of pine from the Mediterranean Spanish forest, Pinus halepensis and Pinus pinaster, were characterized in the laboratory. Chips of the two species showed different moisture and ash contents. Ashes from both species showed an initial deformation temperature above 1100 degrees C in the fusibility test. The ash distribution within each particle size fraction of the bulk was also obtained. The combustion efficiency and emissions in a 50 kW boiler were analyzed and compared with results from a test with pine pellets. The parametric study showed that the excess air in the boiler reduces the gaseous emissions but also the boiler efficiency, while increasing the rate of secondary air had no effects on efficiency, but reduced the CO emissions bellow the EN 14785 limit. (C) 2013 Elsevier Ltd. All rights reserved.