With a view to save fuel, the use of a regenerative burner as a heating source has been spreading in the field of industrial furnaces. By combining a burner with a regenerative air preheater, a second generation regenerative burner the Rotary Regenerative Combustion System (RRX) has been developed, which makes for lower emissions of air pollutants and compactness, in addition to fuel savings. In this paper, heat transfer characteristics of RRX were deduced theoretically based on the heat transfer theory of a regenerative air preheater and investigated experimentally using two test rigs. A commercially operating fired heater was revamped in the summer of 1994 to install 3 sets of RRXs, and it has been sucessufully operated for one year. As a result, it was recognized that the heat transfer rate in a RRX can be predicted within +/-10% of deviation, by considering not only convective but also radiative heat transfer. Furthermore, it was confirmed both theoretically and experimentally that fuel efficiency exceeding 90% was stably attained in a commercialized fired heater. Around 60 ppm of NOx emission (as dry, 6% O-2) was also measured, although the preheated air temperature was calculated as high as 930 K.