welded at their ends to links 92 which are in turn interconnected by means of pins 94 such that the overall track structure 62 is adapted to continuously move over a pair of longitudinally spaced dual sprocket pairs 96 having radially extending teeth 98 which extend between the individual link pairs 92 and in that manner are adapted to either continually or intermittently move by means of a suitable motor 99 generally the track 62 movement is intermittent that is it preferably moves a fraction of an inch every predetermined time period both distance movement and time interval are selected depending upon the type of fuel being burned and the furnace heat requirements similarly the individual fuel pellets are accordingly also timed to enter the combustion chamber 56 via the inlet 70 according to the same criteria as the combustible material is burned it produces an ash or clinker which tends to settle in the lower portion of the material layer being burned that is immediately adjacent or on top of the track 62 also dependent on the type of material being burned and the thickness of the ash or residue layer the gate 100 positioned at the downstream end of the combustion chamber and supported by the end walls 50 as by extension arms 102 in turn adapted to be supported in spacer elements 104 attached to the upper edge of the side walls 44 thus the bottom edge 106 of the gate 100 is adapted robe positioned a distance above the upper surface of the track 62 such that the ash residue remaining thereon passes thereunder while any unburned material is retained for a longer time in the combustion chamber such ash residue simply.