Outdoor air opening and protection.
Municipal Code of Chicago § 18-28-401.6
in effect18-28-401.6 Outdoor air opening and protection.
Air intake and exhaust that terminate outdoors shall be suitably protected against Chicago weather conditions, with corrosion resistant screens, louvers and grilles. Area of the outside air intake shall be sized so that at least 100 percent of the code-required outside air as required in Section 18-28-403.1 can be taken from outside at velocities not in excess of 1,000 feet per minute (304.8 mpm) through free area except for systems defined in paragraph 18-28-403.1.3.
Table 18-28-401.6
Opening Sizes in Louvers Grilles and Screens Protecting Outdoor Exhaust and Air Intake Openings
Outdoor Opening Type | Minimum and Maximum Opening Sizes in Louvers, Grilles and Screens Measured in Any Direction
Exhaust openings | Not less than 1/4 inch and not greater than 1/2 inch
Intake openings in residential occupancies | Not less than 1/4 inch and not greater than 1/2 inch
Intake openings in other than residential occupancies | Not less than 1/4 inch and not greater than 1 inch
For SI: 1 inch = 25.4 mm.
Source: City of Chicago, Municipal Code of Chicago (American Legal Publishing, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/chicago/latest/chicago_il/0-0-0-2686876Fetched: 10/24/2026