Abstract: An improved furnace design for carrying out the catalytic steam reforming of hydrocarbons, including an air delivery and burner system which extends across the top of the furnace. The air delivery system includes a plurality of air ducts each forming a plenum arch, with the arches being suspended between their respective ends as they span the top of the furnace. Burners, for providing heat to the radiant section of the furnace, are spaced within each of such arches and extend into the furnace. Further, the plenum arches provide a supporing structure for the insulation forming the top the radiant section of the furnace.