There are many types of biomass that grow in the Nordic countries, and which are poorly utilized. Examples include hay from green fallows and buffer zones, cereal straw and reeds from lakeshores and coasts. Such biomass could be locally converted into energy via biogas production or through combustion. Our target was to study the suitability of reed canary grass, common reed, buffer zone grass and wheat straw for combustion in a Danish whole round-bale boiler (380 kW, accumulator 70 m3). The boiler is fed with three round bales by a tractor with a front loader, the bales are combusted in 6 8 hours and finally the ashes are removed from the boiler by tractor. For this study, the boiler was equipped with a smoke gas analyser, which can measure flue gas temperature, and CO, CO2, O2, NO and NO2 concentrations. Combustion efficiency can be calculated using these values. The round bales were dry (10 14 %, w.b.) and their density was between 66 131 kg DM/m3, depending on the material. Loose wheat straw bales burnt best (average CO 1356 ppm, NOx 98 ppm, efficiency 79 %). Combustion was poorest with dense reed canary grass bales (average CO 3969 ppm, NOx 50 ppm, efficiency 64 %). Combustion of common reed and buffer zone grass was intermediate. According to ash analyses all materials had sufficiently low heavy metal concentrations that it would be safe to spread the ash on fields. It is not fully clear why reed canary grass and buffer zone grass combusted poorly, but it is probable that the density of the bales was too high for this type of boiler. According to the boiler owner, combustion has been best when the straw bales have been sufficiently loose (< 100 kg DM/m3).