A process for an endothermic reaction includes the steps of carrying out an exothermic reaction in which a fuel is combusted to generate heat for transfer to a feedstock subject to an endothermic reaction, the waste heat from the exothermic and endothermic reactions being transferred to at least three fluid streams within a single heat recovery zone downstream of the endothermic and exothermic reactions, the apparatus therefor being contained within a single vessel.