A turbulent heat-flux model for buoyant flows is derived based on algebraic modeling techniques. Buoyancy terms are included in order to allow for the prediction of counter-gradient transport. The model incorporates a mixed time scale, based on both the velocity and thermal turbulence time scales and relaxes the assumption of a constant turbulent Prandtl number. Thus simplified, the algebraic equations, which are explicit in the heat fluxes, depend explicitly on buoyancy, the mean velocity and thermal fields, the turbulent kinetic energy and its dissipation rate and the temperature variance and its dissipation rate. Nearwall corrections are formulated to make the model asymptotically consistent as a wall is approached and this allows the heat flux equations to be integrated to the wall once the transport of the temperature variance and its dissipation rate and the velocity field are known. The nonbuoyant version of the model has been validated previously, therefore, the present model is applied to near-wall buoyant turbulent flows only. Test cases considered include fully developed horizontal channel flows with a heated bottom wall and turbulent flow in a heated vertical pipe. The prediction of both flow types by the present model are in agreement with experimental data. In view of these results, the present model is found to be capable of capturing the essential physics and yields asymptotically correct results near the wall for both buoyant and nonbuoyant incompressible turbulent flows.