Exhaust hood systems exhausting over what amount of air must have makeup air provided?

In the context of exhaust hood systems, the requirement for providing makeup air is crucial for maintaining balance in indoor air quality and ensuring the efficient operation of the ventilation system. When exhaust systems remove a significant volume of air from a space, it creates a negative pressure which can lead to issues such as reduced indoor air quality, increased energy consumption, and potential problems with backdrafts from other appliances.

The correct choice highlights that exhaust hood systems exhausting over 400 cubic feet per minute must have makeup air provided. This threshold is established to ensure that adequate air supply is present to replace the air being removed, thus preventing negative pressure situations. The provision of makeup air also helps in maintaining comfort levels, controlling humidity, and ensuring that combustion appliances function correctly without being starved of air.

Specifying 400 cubic feet per minute as the critical limit recognizes the significant change in air pressure dynamics that occurs at this level of exhaust and reflects best practices recommended for effective mechanical ventilation in commercial and industrial applications. Hence, recognizing the importance of this threshold is vital for compliant and safe design and operation of exhaust systems.