ABSTRACT A method for quantitatively comparing dissimilar ventilation systems has been developed. A calibrated ventilation model was exercised over a range of parameters seen in new and existing housing in the United States. Varied parameters included climate@ building enclosure air leakage@ presence or absence of a central forced-air space conditioning system@ ventilation system type@ ventilation airflow rate@ and contaminant generation locations. A baseline exposure was established based on the ASHRAE Standard 62.2-2007 ventilation rate using a fully-ducted balanced ventilation system as the reference system and a moderately airtight building enclosure (3.5 ach50). A ventilation airflow coefficient was then determined for each ventilation system such that the occupant exposure using the subject ventilation system was equal to the occupant exposure using the reference system at the baseline ventilation rate. These coefficients can be used to compare the effectiveness of different ventilation systems.