Mercurous Haides (Hg₂X₂:X = Cl, Br) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region which is the driving force for mechanism of PVT, i.e., sublimation-condensation, the thermal buoyancy-driven convection may occur. We investigate the effects of thermal convection on the crystal growthrate in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. Our results show that the growth rate increases linearly with Grashof number for 7.27 x 10⁶ ≤ Gr ≤ 1.14 x 10⁷, and for aspect ratios (transport length-to-height:Ar), 0.2 ≤ Ar ≤ 1.0 sharply increases and for 1.0 ≤ Ar ≤ 20 slowly decreases. The rate decrease exponentially with the partial pressure of component B for Ar = 5 and ΔT = 30K. We have also shown that the magnitude of convection decreases with the aspect ratio (Ar). For gravity levels of less than 10^-2G₀, the non-uniformity of interfacial distribution is negligible.