Duct Detectors Req'd to Connect to Fire Alarm?

3/7/2025

If a duct detector is installed, and the mechanical unit has a capacity of less than 2,000 CFM, it is required by code for the duct detector to be connected to the fire alarm panel?

Alternatively, removing the detectors can be considered in this situation.

Looking for relevant code and standard basis. We're under the 2021 IFC, 2021 IBC, and 2019 NFPA 72. Thank you!

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10 Comments

Glenn Berger

3/7/2025 08:10:30 am

NFPA 90A (2021) Section 6.4.4.2 requires the connection to the building's fire alarm system if one is installed.

Now for the trick part of your question - Since the unit is less than 2000 cfm, then the smoke detector is not required per NFPA 90A, then the provision to connect to the fire alarm system is not required.

Note: I did not check the IBC and IFC requirement in researching my response.

Glenn Berger

3/7/2025 08:12:07 am

One more item - If this was my project, I would still connect all smoke detectors that are installed to the building's fire alarm control panel.

Robert Kessenich

3/7/2025 10:27:45 am

Glenn, I agree with you. If it is installed it should have an acceptance test, operate and signal the same as those that are required.
Non-required smoke alarms and devices need to be maintained if installed.

Sean H

3/7/2025 08:15:11 am

Notably, NFPA 90A is not a referenced standard in the IBC, so you'd be under the purview of the IMC as modified by any locally adopted amendments. If you don't meet the CFM threshold, the unit likely does not require a duct detector. It can still be a bit of a gray area in the eyes of an AHJ if a building is equipped with certain safety features and you want to remove/lessen the amount of safety - it's a good talk with the AHJ to make sure all parties are on board before doing so though.

If a duct detector is installed, and there's a fire alarm system present in the building, then the IMC requires it to be connected to the fire alarm system for supervision.

Todd E Wyatt

3/7/2025 08:16:41 am

The scoping Code (IBC-2021) determines where "duct smoke detectors" (DSD) are located per 907.2.13.1.2.

907.2.13 is for "High-Rise Buildings" so if your Project is not a HRB, DSDs are not required.

If your Project is a HRB but it does not include the (2) conditions per 907.2.13.1.2, DSDs are not required.

REFERENCES
IBC-2021
Chapter 9 Fire Protection and Life Safety Systems
Section 907 Fire Alarm and Detection Systems
907.2 Where Required—New Buildings and Structures
907.2.13 High-Rise Buildings
907.2.13.1 Automatic Smoke Detection
907.2.13.1.2 Duct Smoke Detection
Duct smoke detectors complying with Section 907.3.1 shall be located as follows:
In the main return air and exhaust air plenum of each air-conditioning system having a capacity greater than 2,000 cubic feet per minute (cfm) (0.94 m3/s). Such detectors shall be located in a serviceable area downstream of the last duct inlet.
At each connection to a vertical duct or riser serving two or more stories from a return air duct or plenum of an air-conditioning system. In Group R-1 and R-2 occupancies, a smoke detector is allowed to be used in each return air riser carrying not more than 5,000 cfm (2.4 m3/s) and serving not more than 10 air-inlet openings.

Todd E Wyatt

3/7/2025 08:24:26 am

The reference to 907.3.1 from 907.2.13.1.2 above :

IBC-2021
Chapter 9 Fire Protection and Life Safety Systems
907.3 Fire Safety Functions
907.3.1 DUCT SMOKE DETECTORS
Smoke detectors installed in ducts shall be listed for the air velocity, temperature and humidity present in the duct. DUCT SMOKE DETECTORS shall be connected to the building's fire alarm control unit WHERE A FIRE ALARM SYSTEM IS REQUIRED BY SECTION 907.2. Activation of a DUCT SMOKE DETECTOR shall initiate a visible and audible supervisory signal at a constantly attended location and shall perform the intended fire safety function in accordance with this code and the International Mechanical Code. In facilities that are required to be monitored by a supervising station, DUCT SMOKE DETECTORS shall report only as a supervisory signal and not as a fire alarm. They shall not be used as a substitute for required open area detection.
Exceptions:
1. The supervisory signal at a constantly attended location is not required where DUCT SMOKE DETECTORS activate the building's alarm notification appliances.
2. In occupancies not required to be equipped with a fire alarm system, actuation of a smoke detector shall activate a visible and an audible signal in an approved location. Smoke detector trouble conditions shall activate a visible or audible signal in an approved location and shall be identified as air duct detector trouble.

Darin

3/7/2025 09:54:07 am

Respectfully disagree. Duct detectors are required in many commercial and residential buildings that are not high rise. The scoping code in most jurisdictions related to any hvac requirements is the mechanical code(most jurisdictions adopt the IMC or UMC). Air moving systems that produce is excess of 2000cfm require a shutoff upon detection of smoke via a duct detector or one of the exceptions is via area smoke detection. The only real difference between the UMC and IMC is the duct detector location (UMC requires it on the supply side and the IMC on the return).

To the authors question, when something is installed voluntarily it still shall comply with adopted regulations. So in my opinion, if a fire alarm system is required for said building/occupancy then the DD status shall be monitored by it (supervisory).

Christopher Nelson

3/7/2025 10:09:45 am

I have been told a lot of hvac units have them installed already from the manufacturer and they have to get ripped out for fire alarm duct detectors to be installed. I wonder if this is one of those instances.

Conrad

3/7/2025 11:34:29 am

During fire alarm acceptance testing in our (NFPA) jurisdiction, if duct detectors are installed. If there are voluntarily installed duct detectors, they need to be connected to the fire alarm system.

IFC 2021 talks about this and someone from an IFC jurisdiction can elaborate more.

901.4.2 Nonrequired Fire Protection and Life Safety Systems
Fire protection and life safety systems or portion thereof not required by this code or the International Building Code shall be allowed to be furnished for partial or complete protection provided that such installed systems meet the applicable requirements of this code and the International Building Code.

Keith.O

3/12/2025 10:26:08 am

Another interesting dilemma I often come across between the IMC/UMC and NFPA 90A and NFPA 72 is the issue of where and how many duct detectors are to be installed.

NFPA 72 states on the return side most Mechanical Codes require both supply and return.

Wish the standards were actually standard.

Duct Detectors Req'd to Connect to Fire Alarm?

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