Wood and biomass are considered to be environment friendly resources and their use is thus encouraged. The advantage is evident from comparison of CO2 emissions emerging in the combustion of the biomass and of the fossil fuels. Burning of wood is a reaction when C stored in the wood combines with O from the air and CO2, the same kind as in the process of wood rotting, is released. Also in the combustion of fossil fuels CO2 is released, however, this CO2 was taken from the atmosphere and bound millions of years ago. Although CO2 is not a toxic gas it has a great impact on the greenhouse effect and global warming. In a complete combustion reaction the only products are CO2 and water. Incomplete combustion is undesired. It occurs when there is not enough air available, and results in thick smoke full of soot (CO, CH4, PAH) and poor energy efficiency. Slovenia has signed the Kyoto Protocol and is thereby obliged to reduce its greenhouse gas emissions from the year 1990 by 8 % in the next 5 years (i.e. by 2012).