Heat-transfer coefficients from a fluidized suspension to immersed stainless steel spheres and an aluminum cylinder were studied in a laboratory-scale bubbling fluidized bed using coated and uncoated silica sand particles from a 90-MWth circulating fluidized bed (CFB), as well as a 30-MWth bubbling fluidized bed (BFB). The experiments were carried out for gas-velocity-to-minimum-fluidization-velocity ratios (u/u(mf)) from 1 to 3.5 and mean particle diameters of 350 and 635 mum. The heat-transfer coefficients for the coated particles were lower than those for the uncoated particles in all cases, with the difference between uncoated and coated sand particles being more significant for the CFB material than for the BFB sand.