Experimental investigations are made in a hot circulating fluidized bed unit to study the effect of lateral, and lateral and extended fins together on heat transfer coefficient and on the rate of heat transfer. The circulating fluidized bed (CFB): unit consists of a riser column of 102 x 102 mm in bed cross-section (square), 5.25 m in height with the return leg of the same dimensions: Both liquid petroleum gas and coal are used as the fuel. A mathematical model is also proposed to predict the heat transfer coefficient to a water-wall test section with lateral and extended fins. The model results are compared with the present experimental data and also with those of published literature and a fair agreement has been observed. (C) 1997 Elsevier Science Ltd.