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

Duct Detectors Smoke Detection - NFPA 90A Code Requirements - The Basic Rundown for Field Installations
  • 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 common 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 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:

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 duct work 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 any 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 duct work. 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.

Duct Detectors Smoke Detection - NFPA 90A Code Requirements Conclusion

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 other qualified person on the project.

The Blower Motor – Gas Furnace Components 3

A gas furnace needs to move air across the heat exchanger so enter the gas furnace blower motor. The gas furnace blower motor is usually in the same cabinet as the gas furnace heat exchanger and other parts of the gas furnace. The gas furnace blower motor is usually controlled by the same board which controls the burners and ignition. The same gas furnace system can also be integrated and used with an air conditioning system.

There are some high efficiency systems which utilize a variable speed ECM blower motor. These blower motors use DC current which is supplied by a separate solid state board which contains a rectifier to convert AC voltage into DC voltage. Control of these blower motors and what determines the speed they run at is different from furnace manufacturer to furnace manufacturer.

These variable speed blower motors have the ability to run at different speeds as determined by the control board and the engineering which went into the control board. The other type of blower motor which is in gas furnaces is the PSC or Permanent Split Capacitor blower motor. These blower motors offer good start-up torque and run more efficiently (except the variable speed blower motor) than other types of motors.

Conclusion

Whether the gas furnace has a variable speed blower motor or a PSC blower motor most gas furnaces use direct drive for the blower wheel. A blower wheel is attached to the shaft of the blower and this blower wheel moves the air required to be blown across the heat exchanger and into the ducts of the residence.

To learn more about HVAC and gas heating systems click here.

You may also want to visit some of our other articles to learn HVAC: 4 Wire or 5 Wire Thermostat Wiring Problem | Thermostat Wiring Colors Code | How to Wire a Thermostat | Boiler Circulation Problems Troubleshooting | Hot Water Boiler Sequence of Operation | Daikin Air Conditioner Reviews | Carrier Gas Furnace Reviews | Air Conditioner Breaker Trips

For more on smoke detectors click here.

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Duct Detectors Smoke Detection - NFPA 90A Code Requirements

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