The ventilation airflow rates are generally specified in terms of Air Changes per Hour (ACH). Such specification requires higher airflow rates for larger spaces irrespective of the strength of contaminants. This study with the help of a mass balance approach evaluates the impact of space volume on the contaminant dilution. It indicates that the specification of the same ACH for all space volumes can make smaller spaces vulnerable to a higher dose of contaminant exposure. This study shows that by proportionately adjusting the ACH with the space volume can maintain the same level of dilution (steady state concentration) and occupant exposure for all space volumes, however, larger spaces may take longer time to reach the steady state. The mass balance approach assumes well-mixed conditions within a space and cannot predict the non-uniformity in the breathing zone of occupants which requires a detailed three-dimensional transient Computational Fluid Dynamics (CFD) analysis.