A furnace system includes at least one lower radiant section having a first firebox disposed therein and at least one upper radiant section disposed above the at least one lower radiant section. The at least one upper radiant section has a second firebox disposed therein. The furnace system further includes at least one convection section disposed above the at least one upper radiant section and an exhaust corridor defined by the first firebox, the second firebox, and the at least one convection section. Arrangement of the at least one upper radiant section above the at least one lower radiant section reduces an area required for construction of the furnace system.