The rotary kiln is widely used for the thermal treatment of granular materials in various industries. A better understanding of the heat transfer phenomena, both inside and outside of the industrial rotary kiln, will lead to developing sustainable production techniques, such as materials recycling and heat waste recovery. The present paper summarises two complementary works based on infrared measurements. The first, by Le Guen et al. , was conducted at the industrial scale and sought to correlate the external wall temperature with the thermal behaviour of rotary kilns. The second, by Huchet et al. , was performed at the pilot scale in order to derive the external heat transfer coefficient into heat waste recovery. A combination of these two approaches, based on a physical model of the full system at a large scale, is provided while the inherent energy efficiencies are calculated from the logarithmic mean temperature difference.