The local heat transfer, temperature, and velocity profiles were measured and numerically predicted for the free convection of heat from a vertical constant flux plate to several concentrations of carboxymethylcellulose (CMC) and carboxypolymethylene (Carbopol) powders in water. The fluids were found to have the thermal properties of water and in the shear stress range of interest to follow the power law of Ostwald–de Waele with flow indices varying from 0.395 to 1.0 and with fluid consistencies of 30 to 2300 times that of water. The tests were conducted using either of two plates (12 and 24 in. high) immersed in such a large tank (3000 lb of fluid) that the viscometric properties of the fluid remained unchanged, even for the long test periods used. All fluids, including those with yield stresses and those which suffered free surface effects, were found to transfer heat which could be correlated by the generalized Newtonian correlation Nux=C(Grx*Prx*n)13n+2 which suggests that the precise velocity characteristics of the fluid are of minor importance in determining the heat transfer performance of the system. The numerical solutions, based upon the boundary layer assumptions and the power-law model, were in excellent agreement with the experimental measurements.