The invention provides a nozzle-mixed burner for use in an endothermic process such as hydrogen reforming or ammonia reforming or ethylene cracking or EDC cracking. The burner comprises a fuel duct extending axially through a wall of the furnace. The fuel duct delivers gaseous fuel to an array of nozzles extending laterally to spray the fuel outwardly into an annular chamber defined by a cap. Combustion air is delivered to the chamber by way of a primary air duct. A convergent-divergent section of the duct and an outwardly divergent section of the chamber together form a radially extending venturi. Combustion of the fuel, supplemented by the venturi effect, draws the air through the duct by natural inspiration.