Common supply and return air systems.
Municipal Code of Chicago § 18-28-606.2.2
in effect18-28-606.2.2 Common supply and return air systems.
Where multiple air-handling systems share common supply or return air ducts or plenums with a combined designed capacity greater than 2,000 cfm (0.9 m 3 /s), the return air system shall be provided with smoke detectors in accordance with Section 18-28-606.2.1.
Exception: Individual smoke detectors shall not be required for each variable air volume (VAV) zone unit or VAV-type fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m3/s) and will be shut down by activation of one of the following:
1. Smoke detectors required by Sections 18-28-606.2.1 and 18-28-606.2.3.
2. An approved area smoke detector system located in the return air plenum serving such units.
3. An area smoke detector system as prescribed in the exception to Section 18-28-606.2.1.
In all cases, the smoke detectors shall comply with Sections 18-28-606.4 and 18-28-606.4.1.
Source: City of Chicago, Municipal Code of Chicago (American Legal Publishing, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/chicago/latest/chicago_il/0-0-0-2687654Fetched: 10/24/2026