AbstractThe work described in the paper is concerned with the measurement of the flow of tracer gas and aerosol particles in rooms. Measurements were carried out in single‐ and two‐zone systems using SF6tracer gas and oil‐smoke particles. Initial tests were carried out in a single‐zone system using different arrangements of window opening. Results indicated that tracer‐gas exchange rates were generally higher than particle exchange rates. This was due to the fact that the ventilation air entering the zone contained a significant concentration of particles but a negligible quantity of tracer gas. The exchange rates of tracer gas and smoke particles through a doorway were also measured in a two‐zone system. The doorway coefficients of discharge were calculated using a theory based on the Bernoulli equation. The coefficients of discharge for the opening were in the range 0.4–0.96 for tracer gas measurements and 0.15–0.42 for smoke‐part