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What you will learn from Duct Detectors Smoke Detection - NFPA 90A Code Requirements article:

  1. Preface for the NFPA 90A requirements for duct detectors in air conditioning and heating equipment.
  2. The question: Where do you install duct detectors in ductwork?
  3. a detailed answer to satisfy requirements
  4. exclusions and exceptions to the requirement
  5. references for further information about HVAC equipment and fire safety
  6. Finally, additional related information about fire and smoke dampers regarding HVAC

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

Duct Detectors Smoke Detection - NFPA 90A Code RequirementsDuct Detectors Smoke Detection - NFPA 90A Code Requirements - This article references the current NFPA 90A “Standard for the Installation of Air-Conditioning and Ventilating Systems” and provides basic instruction on the installation of smoke detectors inside the ductwork. NFPA 90A is specific to Air Conditioning and Heating Systems installation. The purpose of the NFPA 90A is to prevent the spread of smoke and fire through ductwork and ventilation systems for air conditioning and heating systems with high capacities. Always ensure you check the latest codes for current information. Additionally, some municipalities have more stringent codes in place. Therefore, it is wise to check local code requirements in addition to current national codes.

Get your copy here: NFPA 90a: Standard for the Installation of Air-Conditioning and Ventilating Systems

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

Question: Where to place smoke detectors in the ductwork on commercial projects to comply with code? In this case the NFPA 90A requirements for HVAC systems and ductwork. The NFPA 90A is specific in defining the position of the duct smoke detectors in the ductwork. The code details why smoke detectors are required along with the intentions of installing duct smoke detectors inside the ductwork to comply with code requirements. The question is: Where do you install these devices in the ductwork?

The Basic Rundown for Field Installations | Where are Smoke Duct Detectors Required?

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

  • In air supply systems with a capacity greater than 2000 CFM’s downstream of the air filters and upstream of any branch ducts.
  • In multi-story buildings at each story with a commonly shared return and having a capacity greater than 15,000 CFM’s. The smoke detection device should be installed before the connection to the common return and before any connection to any recirculation or fresh air inlet in the return air systems. The code includes plenums where the plenum is used for a common return.

Duct Smoke Detection - NFPA 90A Code Requirements – There are exceptions to the two basic requirements:

  • Ventilation fan systems used to remove air from the inside of the building to the outside of the building. These fans are excluded from the above requirements and
  • Return air smoke detectors are not required when there is a protection of the space served by a system of area smoke detectors.

Commercial Duct Systems and Fire Safety
Additional references to smoke detector safety in air conditioning and heating systems installation can be found using the following resources:

  • ASHRAE Handbook and Product Directory, “Fire and Smoke Control”
  • The Joint Commission/NFPA Life Safety Book for Health Care Organizations
  • U.L. Standard 269A, Standard for Smoke Detectors for Duct Applications

NFPA 90a Duct Smoke Detector Requirements

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

NFPA 90A Code Requirements - Large 2000 CFM VAV Air Handling Unit - Life and Safety SystemsIn addition to the installation requirements for smoke dampers and fire dampers, the code requirement for any safety devices in ductwork ventilation systems is necessary for basic life and safety. Engineering drawings typically have the location of installation to comply with code requirements. Engineering drawings do not always represent these details. Following up with a Request for Information can hold the job up sometimes.

Additionally, a good technician will educate themselves on the proper installation of an essential component. And especially for the installation of air conditioning and heating equipment and components required by code. Always read the manufacturers instructions, guidelines, and recommendations when installing and testing smoke detectors in ductwork. Special requirements for installation and successful operation makes it necessary for a trouble-free installation. Remember, others will be testing installation including the code inspector, fire inspectors and commissioning people.

Why are Smoke Duct Detectors Required on the Supply Side as noted above?

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

I’ve had this question asked of me several times. While I am a licensed Master HVAC contractor I am not a code official but here is my answer. What happens when a fan motor catches fire or starts smoking before it catches on fire but continues to operate in some capacity? Of course, the answer is simple. It spreads smoke that can harm the occupants of the facility where it is located. I’ve seen bearings seize up and belts spew out smoke until they eventually fail and break.

In the meantime, smoke is being spread throughout the supply side and into the facility where people occupy the rooms. A smoke duct detector on the supply side will do two things provided it is wired and controlled properly. First, it will send an alarm to alert facility operator and maintenance staff. Secondly, it will kill the fan so it does not continue to spread smoke before catastrophic failure of the fan occurs.

There seems to be a conflict in the codes from the NFPA 90A and the International Mechanical Code. It is required in the NFPA 90A but not in the Mechanical Code. Anyone with further comments on this please leave a comment below.

Wiring Diagrams for Duct Smoke Detectors

Firstly, it is important to follow all the instruction provided with the new duct detector. Always follow duct detector manufactures instructions and code for wiring. The wiring diagram graphics here are for illustration purposes only. Of course, everything should be tested multiple times by different authorities to ensure proper sequence of operation. Lastly, the goal is to detect smoke, shut off the fans, and send out an alarm. Finally, always follow all safety instructions which include code and manufacturers instructions.

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

Whenever smoke is detected the fan(s) should be wired to shut down.

Duct Smoke Detectors wiring diagram

Depending on how the controls are set up will depend on which contacts you use. Normally Open or Normally Closed

Conclusion - Duct Detectors Smoke Detection - NFPA 90A Code Requirements

Duct Detectors Smoke Detection Installation

Furthermore, intentions for using duct smoke detectors should not be a substitute for area smoke detectors. Nor should it serve as an early warning detection system. Therefore, they should complement the buildings fire detection system and not serve as the primary fire detection system. Additionally, always follow the code requirements for each project. If you do not understand the code or the requirements ask the engineer or another qualified person on the project.

Get your copy here: NFPA 90a: Standard for the Installation of Air-Conditioning and Ventilating Systems

High Performance HVAC - Air Conditioning and Heating Systems Information

Duct Detectors Smoke Detection - NFPA 90A Code Requirements

Resource: The Fundamentals of HVAC Direct Digital Control


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