NFPA 90A requires supply-side smoke detection on HVAC systems with a capacity of at least how many CFM?

• A. 1000 CFM
• B. 2000 CFM
• C. 5000 CFM
• D. 10000 CFM

Answer: (B)

Supply-side smoke detection is used to catch smoke before it can be pushed through ductwork, helping to contain a fire and limit smoke spread to other spaces. NFPA 90A requires detectors on the supply side of HVAC systems that move at least 2,000 CFM. The rationale is that when a system moves air this quickly, smoke can be drawn into and distributed through the ducts, increasing risk to occupants and complicating firefighting efforts. Having a detector in the supply duct allows an early alarm and, if connected, automatic actions like shutting down the fan or closing dampers to create a barrier against smoke spreading. Smaller systems move air more slowly, so the potential for rapid ductborne spread is lower, and the code does not mandate supply-side detectors there.