What is the design capacity in cfm that necessitates installing smoke detectors in return air risers?

Installing smoke detectors in return air risers is a critical safety measure that helps in early detection of smoke or fire within a building's HVAC system. In the context of mechanical codes, the design capacity at which these detectors must be installed is important for ensuring compliance with safety regulations.

The correct answer indicates that when the design capacity of the air handling system reaches 15,000 cubic feet per minute (cfm), it becomes necessary to install smoke detectors in the return air risers. This threshold is established because larger air volumes can spread smoke more rapidly through a building's ventilation system, potentially allowing for quicker and more widespread fire hazards. By requiring smoke detectors at this capacity, it ensures that any presence of smoke is detected early, enhancing safety protocols and allowing for prompt action to mitigate risks.

Designing systems with this consideration not only complies with code requirements but also reflects best practices in building safety management. It accounts for the dynamics of smoke movement within duct systems and contributes to comprehensive fire protection strategies.