In general, the combustion of renewable biomass only releases as much carbon dioxide as the plants absorbed and fixed from the atmosphere while they were growing. However, if the carbon footprint is to really be this balanced, the biomass must be cultivated and the land used in a sustainable way. Deforestation, for instance, has a negative impact on the carbon footprint. If, however, the amount of wood burned does not exceed the amount that can grow back, the whole process is carbon neutral.
Saskia Blank of the Ideas 2020 team answered this question.