This paper presents the background and development of the reradiant concept for the radiant stack type recuperator. It also presents the results of an ongoing demonstration program of this concept.IGT developed the concept of the reradiant recuperator which increases the effectiveness of conventional radiant recuperators by 5 - 15% depending on unit size. This paper discusses the mathematical model developed by IGT which optimized the application of a metal leaf type insert within the hot gases passing through a conventional radiant recuperator. The metal leaf insert is designed to maximize radiation to the annulus wall. This increase in heat transfer is not due to increased convective heat exchange, as when a “core buster” insert is used, but strictly due to radiation from the leaf insert.Data on a prototype unit operated by IGT to verify the mathematical model will be presented and explained. Data collected from the present ongoing demonstration program (i.e., reradiant recuperators installed on industrial furnaces) will provide current data on the program.