A process heater system (10) for an industrial envelope (11) comprises a main combustion chamber (20), an afterburner (30), and an exhaust stack (40). Retrofitted heat-recovery piping (50) receives combustion gas downstream of the afterburner (30) and uses it as a heat source for the industrial envelope. When the industrial load in the main combustion chamber (20) is paint, powder coating, varnish, epoxy, grease and/or oil, the secondary materials burned in the afterburner 30 can be considered alternative fuel, not solid wastes.