A method operates a furnace unit with a feed chute and a camera for capturing an image of the surface of the chute. The chute includes a slide on which material flows to a grate, and the coverage of the chute and in particular of the slide with material, the burning bed thickness and the burnout zone are determined by an image evaluation.

A wood pellet stove operable to mount to a wall includes a combustion chamber, a combustion chamber door, and a hopper. The combustion chamber has a front, back, and side. The combustion chamber door is in the front of the combustion chamber. The hopper is mounted at the side of the combustion chamber. The bottom of the hopper is below a top of the combustion chamber, and a top of the hopper is substantially coplanar with the top of the combustion chamber. The stove may also include a sight glass or fuel level monitoring system for determining a fuel level of the hopper without opening the hopper.

A method for processing material that contains biomass. The material is led onto a conveyor. The conveyor conveys the material to an apparatus for mechanical processing and/or to a further processing plant. The moisture content is measured and/or the size of pieces of non-combustible material and/or the content of non-combustible material in the material flow is measured in connection with the conveyor. Based on at least one of the measurements, material is conveyed to the material to be conveyed for further processing and/or to the apparatus for mechanical processing, or to at least one material to be conveyed elsewhere than to the further processing plant or the apparatus for mechanical processing. Also a system for processing material that contains biomass.