We demonstrate the specific non-Boussinesq roles played by various fluid properties in thermal convection by allowing each of them to possess, one at a time, a temperature dependence that could be either positive or negative. The negative temperature dependence of the coefficient of thermal expansion hinders effective thermal convection and reduces the Nusselt number, whereas the negative dependence of fluid density enhances the Nusselt number. Viscosity merely smears plume generation and has a marginal effect on heat transport, whether it increases or decreases with temperature. At the moderate Rayleigh number examined here, the specific heat capacity shows no appreciable effect. On the other hand, the conductivity of the fluid near the hot surface controls the heat transport from the hot plate to the fluid, which suggests that a less conducting fluid near the bottom surface will reduce the Nusselt number and the bulk temperature. © EPLA, 2009.