64 through which the forced or compressed air enters a distribution manifold 66 for delivery to the burning fuel within the combustion chamber 26 the air distribution manifold 66 includes two vertically oriented c shaped conduits 68 positioned on each side of the combustion chamber 26 proximate side walls 14 and 16 each of the c shaped conduits 68 has a bottom leg 70 a vertical leg 72 and a top leg 74 a horizontal connector leg 76 joins the c shaped sections together and itself is in fluid communication with the outlet 64 of plenum 58 the legs 70 72 74 and 76 are hollow formed of metallic tubing having either a square or circular cross section and in fluid communication with one another so as to permit the passage of air therebetween each bottom leg 70 is disposed adjacent the bottom wall 24 and the respective ends of bottom leg 70 are positioned near the front and rear walls 18 and 20 extending upwardly from the front end of each bottom leg 70 and positioned adjacent the front wall 18 is a vertical leg 72 for conducting air to the top leg 74 the top leg 74 is disposed adjacent the top wall.