A study of free convective turbulent heat transfer between parallel plates has been made. The initial flow is assumed to remain laminar until a combination of geometry, temperature, and flow rate conditions reach a pre-defined level. At this point the model used in this study assumes transition and permits laminar flow to gradually develop into fully turbulent flow. Turbulent flow characteristics are predicted by a mixing length model which incorporates empirical parameters used in the literature. Using air as the fluid, a wide range of channel geometries, relative surface temperatures, and flow rates have been examined. Guided by the very limited available experimental data, computations were made and several correlations were developed to enable important quantities to be estimated given the channel geometry, surface temperatures, and inlet air temperature.