Experimental data on the heat transfer coefficients from a bubbling fluidized bed burner toward water-cooled confining walls placed above the free surface of the bed are scarce. The present work is an attempt to cover this gap. Experiments were carried out in a laboratory scale fluidized bed reactor that was equipped with a double pipe heat exchanger located above the bubbling bed region. The bed was composed of silica sand particles and five different sizes were tested107.5, 142.5, 180, 282.5, and 357.5 m. The bed operating temperature ranged from 700C to 820C. Under these circumstances, heat is transferred to the membrane walls through three mechanisms: convection from the gas-solid flow, radiation from the bed surface or from the flame, and projection of solid particles away from the bed toward the confining walls. A correlation for the global heat transfer coefficient is proposed with an average deviation of 20%.