passage whose sides are formed by upper portions 26 of side rails 28 the top of a fire grate 30 which is angled downward 31 typically at an angle of 14 u00b0 to 22 u00b0 most preferably at 18 which ensures that the coal will not heap or run away over the fire grate which has a multiplicity of air holes 32 disposed therethrough the grate forms the top 34 of an air box 36 which is forced air fed with typically a 100 cfm squirrel cage blower 38 whose air intake is made variable by a swivel cover plate 40 the blower is sealed at its output end to the intake of the air box by a gasket 42 the pusher assembly is rectangular box shaped and has an upper casting 44 forming a top 46 and three sides 48 the side away from the flange 50 being open and holding a mounting 51 for a stroke adjusting screw 52 bolted to the upper casting is a bottom plate 54 which has centrally disposed thereon a rectangular slot 56 the plate which is somewhat longer than the top casting so as to form a step like protuberance 58 at its flange side edge encloses a pivotally mounted 59 angle bar 60 whose angle is adjusted by the stroke adjusting screw and which is intermittently in contact with cam 64 seated inside the pusher.