An investigation was performed to study the emissions of state of the art Small-scale residential heating appliances. The different combustion systems Were compared at optimal combustion conditions. A comprehensive characterization of released organic species of all combustion systems was performed. An approach Was performed to estimate the toxicity of the emitted particulate matter by the content of polycyclic aromatic hydrocarbons (PAHs). It is based on the proposal of the German Research Foundation (DFG) that the health risk is proportionally summarized by different PAHs with different health risk potentials. This approach allows for a rough but fast comparison of different furnaces by the Calculation of the toxic equivalent (TEQ) value in addition to the emission of particulate matter (pm). Best results Were obtained by combusting wood as pellets in a modern pellet boiler (PM = 11-13 mg MJ(-1) and TEQ = 0:12-0.75 mu g MJ(-1)). On the opposite of the emission scale, the toxic potentials of the typical log wood stave were found to be about 2 orders of higher (pm = 67-119 mg MJ(-1) and TEQ = 14-28 mu g MJ(-1)) compared to the pellet boiler, despite optimized combustion conditions.