Duct Smoke Detectors

  • A duct smoke detector is a device or group of devices used to detect the presence of smoke in the airstreams of ductwork sections of the HVAC air-handling systems in industrial, commercial or large institutional facilities.
  • Duct smoke detection not only serves to assist in preventing the spread of toxic smoke and combustion gases, it can also be used to assist in protecting property and equipment.
  • Purpose of Duct Smoke Detectors
    • Primary Purpose: Prevent injury, panic and property damage by reducing the spread of smoke
    • NFPA 90A: Prevent the distribution of smoke through the supply air duct system and exhaust outside
Codes and Applications
  • NFPA 72 Installation guidelines : Duct smoke detectors shall be installed in all new and replacement air handling units, air conditioning units, package units and fans where required by NFPA 90A and NFPA 101.
    • Systems capable of 2,000 CFM (5 ton cooling) require supply-side detectors
    • On systems over 15,000 CFM, supply and return detectors are required
  • When activated duct smoke detectors shall:
    • Stop their respective fan(s)
    • Cause an audible and visible signal in an approved location to indicate a detector trouble condition
    • Initiate fire smoke dampers
  • Note: Duct smoke detectors are not intended to initiate a general evacuation
Principles of Operation
  • Duct smoke detectors work by creating a pressure differential between the sampling tube and exhaust tube on the housing to draw air from the duct.
  • When the duct smoke detector senses smoke, the:
    • Fan system will be turned off (N.C. contacts)
    • Trouble alarm signal will be initiated (N.O. contacts)
Typical Installations in HVAC Systems
  • Smoke detector mounted on the duct
  • Smoke detectors in NC packaged units
  • Rooftop installation
  • Smoke detector on fire smoke dampers