A novel combustion airstream control concept has been developed based on in situ sensors for combustion temperature, residual oxygen concentration and residual un-combusted CO / HC components. The implementation of this control concept allows for a large reduction in toxic gas emissions by up to 80 % compared to hand-operated furnaces. A stable long-term CO / HC sensor for such an application is not available; thus, the long-term sensor signal stability of different CO / HC sensors is studied.