The influence of thermal buoyancy on transfer of heat and fluid flow across six inline heated square cylinders is investigated using two-dimensional thermal lattice Boltzmann method. For the conditions 0 ≤ Ri ≤ 2.0, Pr= 0.71, s/d = 1.5, and Re = 100 numerical results were reported. The isotherms plots and vorticity contours are used to depict thermal fields and overall flow patterns. The variation of integral heat transfer parameters like average Nusselt number is determined to understand the significance of the Richardson number on transfer of heat and fluid flow. The major finding from this numerical work is that heat transmission process becomes unsteady periodic under the impact of Richardson number and is highly transient. The transitions in heat transfer can be explained through temperature contours and Nusselt number signals. The vortex shedding frequency contributes substantially to transfer of heat from the cylinders. Temperature contours, average Nusselt number time series, and associated power spectra are used to roughly demarcate the three heat transfer regimes.