This research numerically investigates the effect of make-up air on the smoke conditions in an atrium under different make-up air velocities and fire sizes. A total of twenty-four (24) simulations were conducted using the Fire Dynamics Simulator (FDS) to consider different scenarios of fire located at the center (axisymmetric), northwest corner and southeast corner of the atrium. Fire sizes of 1 MW, 3 MW and 5 MW along with different make-up air velocities of 1 m/s, 1.5 m/s, 2.5 m/s and 3.5 m/s were simulated to investigate their effect on smoke conditions the atrium. The results showed that the simulation predicted slightly higher temperatures and lower smoke layer heights when compared to the experimental tests. The position of the fire source at different locations showed different and increasing temperatures when the velocity changes from 1 m/s to 3.5 m/s, however the effects of make-up air velocities were minor.