Duct Smoke Detectors for Supply vs Return - CALIFORNIA

Does California require Duct Smoke Detectors on the Return Side?

Since this question comes up so often, I felt it would be beneficial to put an article together with the answers and applicable code/standard references. Please note that the below information is pertinent to CA and may be altered by individual jurisdictions if they have formally adopted a local ordinance to supersede the state level requirements.

 There are two items to cover with this topic:

1. In California, are we required to install the duct smoke detector on the supply or return side of HVAC units GREATER than 2,000 cfm?
2. In California, are we required to install a duct smoke detector on both the supply and return side of and HVAC unit GREATER than 15,000 cfm? 

Before we can answer these questions, we need to know what codes and standards California has adopted. 

Chapter 35 of the California Building Code 2022 edition is dedicated to clarifying which codes and standards are adopted by the State Fire Marshal. The code/standard references are on the left with vertical columns signifying which agencies have adopted them. The third column from the left with the “Xs” is for the State Fire Marshal. From here we can tell that based on the 2022 CBC, the applicable standard for Fire Alarm is the 2022 edition of NFPA 72. Please also note that the IMC or International Mechanical Code is not found within this document.  This lets us know this code not valid in California and therefore its individual language does not apply.

2022 CBC MATRIX ADOPTION TABLE - CHAPTER 35

Duct Smoke Detectors based on NPFA 72 2022 Edition

NFPA 72 2022 Section 17.7.5.3.1 States “To prevent the recirculation of dangerous quantities of smoke, a detector approved for air duct use shall be installed on the supply side of air handing systems as required by NFPA 90A and 17.7.5.4.2.1”

Duct Smoke Detectors based on NFPA 90A

 Since NFPA 90A is referenced in the above NFPA 72 standard, it shall apply. The language for this standard is found in section 6.4.2.1 and reads as follows:

 “Smoke detectors listed for use in air distribution systems shall be located as follows:

1. Downstream of the air filters and ahead of any ranch connections in air supply systems having a capacity greater than 2000 cfm.
2. At each story prior to the connection to a common return and prior to any recirculation or fresh air inlet connection in air return systems having a capacity greater than 15,000 cfm and serving more than one story.”

Duct Smoke Detectors based on the International Mechanical Code (IMC)

NO Duct Smoke Detector on Return for units greater than 2,000 cfm in California

 The code that requires a duct smoke detector in the return side of a unit greater than 2,000 cfm is the International Mechanical Code. Keep in mind since this code is not a referenced standard in the California Building Code, it does not apply.

 Section 606.2.1 of the International Mechanical Code states a duct smoke detector shall be installed in return air systems with a deign capacity greater than 2,000 cfm.

Summary 

• NFPA 72 2022 17.7.5.3.1 - In California we are required to provide a duct smoke detector on the SUPPLY side of HVAC units per NFPA 90A.
• NFPA 90A 6.4.2.1 - In California we are required to provide a duct smoke detector on the SUPPLY side of HVAC units greater than 2,000 cfm
• NFPA 90A 6.4.2.1 – In California we are required to provide a duct smoke detector on each return inlet prior to a common return for HVAC units greater than 15,000 which serve more than one floor (below is a simple diagram showing this setup.)
• IMC 2021 606.2.1 – Requires a duct smoke detector in the return of HVAC units greater than 2,000 cfm. THIS DOES NOT APPLY IN CALIFORNIA