Suspension-to-membrane-wall heat transfer was studied in a pilot scale circulating fluidized bed combustor at 700 and 800 degrees C for suspension densities of 10-70 kg/m(3) with 286 mu m silica sand particles. The total suspension-to-membrane-wall heat transfer coefficient is determined using the exposed-pipe-radial, insulated-pipe-tangential, fin one-dimensional heat transfer model of Bowen et al. [B.D. Bowen, M. Fournier, J.R. Grace, Heat transfer in membrane waterwalls, Int. J. Heat Mass Transfer 34 (1991) 1043-1057]. Suspension-to-pipe and suspension-to-fin transfer is also determined from temperatures measured by embedded thermocouples. The fin accounted for about one third of the total heat transfer, and most of this portion passed through the insulated portion of the pipe. (C) 2000 Elsevier Science Ltd. All rights reserved.