Abstract: A fired heater is adapted for increasing the output of a plant where the furnace capacity is considerably improved without corresponding increase in the pressure drop. The described technique utilizes a parallel thermal path in contrast to the conventional series thermal path for heating a hydrocarbon fluid. The fluid is divided into at least two paths where the fluid in the first path is heated primarily by radiation heat transfer mechanism and the fluid in the second path is heated primarily by convection heat transfer mechanism. The at least two fluid streams may then be combined to continue with other desired processing of the fluid.