ASHRAE standard 62 states that air removed from an area with environmental tobacco smoke shall not be recirculated into ETS-free air. A space with ETS requires more ventilation to achieve similar perceived air quality to that of a non-smoking environment.
The amount of ventilation in an ETS area is equal to the amount of an ETS-free area plus the amount V, where:
V = DSD × VA × A/60E
*V = recommended extra flow rate in CFM (L/s)
*DSD = design smoking density (estimated number of cigarettes smoked per hour per unit area)
*VA = volume of ventilation air per cigarette for the room being designed (ft/cig)
*E = contaminant removal effectiveness