What is the ventilation rate?

• A. The amount of indoor air recirculated.
• B. The humidity level in the space.
• C. The amount of outdoor air supplied per unit time.
• D. The temperature of outdoor air.

Answer: (C)

Ventilation rate is the amount of outdoor air brought into a space over a period of time, typically measured as volume per time (like cubic feet per minute or liters per second). This rate matters because it determines how effectively outdoor air dilutes indoor pollutants and maintains air quality. Among the options, describing the amount of outdoor air supplied per unit time is the correct definition, since it directly quantifies how much fresh air is being introduced. The other options refer to humidity, indoor air recirculation, or the temperature of incoming air, which do not define the rate at which outdoor air is supplied.