Free convective heat transfer inside a vertical channel was studied both experimentally and numerically. An experimental model of an isothermally, asymmetrically heated vertical channel was constructed to study various cases of opposing buoyancy forces. Many studies in the literature have investigated buoyancy forces in a single direction. The study presented here investigated opposing buoyancy forces, where one wall is warmer than the ambient and the other wall is cooler than the ambient. Five different temperature ratios were studied using four different channel spacings between the two channel walls. A Mach-Zehnder interferometer provided temperature field visualization. In addition, local and average heat transfer measurements were made with the interferometer. Flow visualization was conducted to determine the flow pattern inside the channel. The measured local and average Nusselt number data were compared to numerical solutions obtained using ANSYS FLUENT. A steady laminar model and a steady k-ε turbulence model with two different wall functions were used. Numerical solutions were obtained for a Prandtl number of 0.71 and Rayleigh numbers ranging from the laminar fully developed flow regime to the turbulent isolated boundary layer regime.