Abstract: An apparatus for the combustion and/or decomposition of fuel by heat, especially of solid fuels such as peat, coal, wood, straw or garbage, comprising a fuel supply and air supply to a bar grate which is used as combustion site and cooperates with material loosening means in the form of disks, prongs or the like which extend through the grate interstices and are mounted on a support member which extends transversely to the grate bars, in which the disks are reciprocable relative to the grate bars in the direction towards the same. The material loosening disks are fitted onto support members each in the form of a support rod of substantially rectangular cross-section such that the disks are individually displaceable in the direction of the support rod.