To investigate effects of the inflow rate on pool boiling heat transfer in a vertical annulus, the inflow area at its bottom has been changed from 0 to 1060.26 mm(2). For the test, a heated tube of 16.5 mm diameter and water at atmospheric pressure has been used. To elucidate effects of the inflow area on heat transfer results of the annulus are compared to the data of a single unrestricted tube. The change in the inflow rate at the bottom of the annulus results in variation in heat transfer coefficients. When the inflow area is 176.71 mm(2) the deterioration point of heat transfer coefficients gets moved up to the higher heat fluxes because of the convective flow at the bottom regions. (c) 2006 Elsevier Ltd. All rights reserved.