Effects of lateral heating on flow profiles and growth rates during the growth of mercurous chloride crystals by the physical-vapour-transport process in vertical ampoules are investigated by a two-dimensional model. The growth conditions of an experimental study available in the open literature are simulated. Lateral thermal boundary condition is modelled by a spatially sinusoidal heat flux. The results of the present computations are in agreement with the earlier experimental results and indicate that an increase in the lateral heating rate can cause a significant decrease in the transport rate while the flow accelerates. In the case of flow bifurcations, the growth rates can become as low as in the case of convectionless flow conditions.