A cracking furnace construction includes a firebox defining a chamber having a high emissivity thermal protective coating disposed on at least part of the refractory walls and/or on process tubes disposed within the chamber. The coating contains an inorganic adhesive for metal/alloy tubes or colloidal silica and/or colloidal alumina for refractory walls or ceramic tubes, a filler, and one or more emissivity agents. A method of coating the firebox chamber includes preparing the surface of the tubes/refractory walls, preparing the coating, and applying the coating to the surface.