Changes in local pool boiling heat transfer coefficients on the outside surface of a $51mmdia$ horizontal tube have been investigated experimentally in water at atmospheric pressure. The local values were determined at every $45deg$ from the very bottom to the uppermost of the tube periphery, and a representative value was suggested. The maximum and the minimum local coefficients were observed at the azimuthal angles of 45 and $180deg$, respectively, from the tube bottom. The coefficient at $90deg$ can be suggested as the representative of the coefficients. The major mechanisms affecting heat transfer on the surface were liquid agitation and bubble coalescence. Moreover, it is identified that the data can be curve fitted as $hb=C1+C2q″$.

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