Natural convection heat transfer in convergent vertical channels has been investigated both by experiments and by numerical solutions of the conservation equations. The investigation encompassed half angles of convergence between 0 (parallel-walled channel) and 15°, and the working fluid was water (Pr ∼5). The channel walls were maintained at a uniform temperature which exceeded the ambient temperature, thereby giving rise to an upflow through the channel. It was found that the Nusselt numbers for the convergent channels could be brought into very close agreement with those for the parallel-walled channel by employing correlation variables based on the maximum interwall spacing as the characteristic dimension. The experimentally determined and numerically predicted Nusselt numbers were in excellent agreement, both in magnitude and with regard to all observable trends.