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  • CHAPTER6
    DUCT SYSTEMS  

    SECTION601
    GENERAL

    601.1 Scope.

    Duct systems used for the movement of air in air-conditioning, heating, ventilating and exhaust systems shall conform to the provisions of this chapter except as otherwise specified in Chapters 5 and 7.

    Exception: Ducts discharging combustible material directly into any combustion chamber shall conform to the requirements of NFPA 82.

    [BF]601.2 Air movement in egress elements.

    Corridors shall not serve as supply, return, exhaust, relief or ventilation air ducts.

    Exceptions:

    1. 1.Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such corridors, including toilet rooms, bathrooms, dressing rooms, smoking lounges and janitor closets, shall be permitted, provided that each such corridor is directly supplied with outdoor air at a rate greater than the rate of makeup air taken from the corridor.

    2. 2.Where located within a dwelling unit, the use of corridors for conveying return air shall not be prohibited.

    3. 3.Where located within tenant spaces of 1,000 square feet (93 m2) or less in area, use of corridors for conveying return air is permitted.

    4. 4.Incidental air movement from pressurized rooms within health care facilities, provided that the corridor is not the primary source of supply or return to the room.

    [BF]601.2.1 Corridor ceiling.

    Use of the space between the corridor ceiling and the floor or roof structure above as a return air plenum is permitted for one or more of the following conditions:

    1. 1.The corridor is not required to be of fire-resistance-rated construction.

    2. 2.The corridor is separated from the plenum by fire-resistance-rated construction.

    3. 3.The air-handling system serving the corridor is shut down upon activation of the air-handling unit smoke detectors required by this code.

    4. 4.The air-handling system serving the corridor is shut down upon detection of sprinkler waterflow where the building is equipped throughout with an automatic sprinkler system.

    5. 5.The space between the corridor ceiling and the floor or roof structure above the corridor is used as a component of an approved engineered smoke control system.

    [BF]601.3 Exits.

    Equipment and ductwork for exit enclosure ventilation shall comply with one of the following items:

    1. 1.Such equipment and ductwork shall be located exterior to the building and shall be directly connected to the exit enclosure by ductwork enclosed in construction as required by the International Building Code for shafts.

    2. 2.Where such equipment and ductwork is located within the exit enclosure, the intake air shall be taken directly from the outdoors and the exhaust air shall be discharged directly to the outdoors, or such air shall be conveyed through ducts enclosed in construction as required by the International Building Code for shafts.

    3. 3.Where located within the building, such equipment and ductwork shall be separated from the remainder of the building, including other mechanical equipment, with construction as required by the International Building Code for shafts.

    In each case, openings into fire-resistance-rated construction shall be limited to those needed for maintenance and operation and shall be protected by self-closing fire-resistance-rated devices in accordance with the International Building Code for enclosure wall opening protectives. Exit enclosure ventilation systems shall be independent of other building ventilation systems.

    601.4 Contamination prevention.

    Exhaust ducts under positive pressure, chimneys and vents shall not extend into or pass through ducts or plenums.

    Exceptions:

    1. 1.Exhaust systems located in ceiling return air plenums over spaces that are permitted to have 10 percent recirculation in accordance with Section 403.2.1, Item 4. The exhaust duct joints, seams and connections shall comply with Section 603.9.

    2. 2.This section shall not apply to chimneys and vents that pass through plenums where such venting systems comply with one of the following requirements:

      1. 2.1.The venting system shall be listed for positive pressure applications and shall be sealed in accordance with the vent manufacturer’s instructions.

      2. 2.2.The venting system shall be installed such that fittings and joints between sections are not installed in the above ceiling space.

      3. 2.3.The venting system shall be installed in a conduit or enclosure with sealed joints separating the interior of the conduit or enclosure from the ceiling space.

    601.5 Return air openings.

    Return air openings for heating, ventilation and air-conditioning systems shall comply with all of the following:

    1. 1.Openings shall not be located less than 10 feet (3048 mm) measured in any direction from an open combustion chamber or draft hood of another appliance located in the same room or space.

    2. 2.Return air shall not be taken from a hazardous or insanitary location or a refrigeration room as defined in this code.

    3. 3.The amount of return air taken from any room or space shall be not greater than the flow rate of supply air delivered to such room or space.

    4. 4.Return and transfer openings shall be sized in accordance with the appliance or equipment manufacturer’s installation instructions, ACCA Manual D or the design of the registered design professional.

    5. 5.Return air taken from one dwelling unit shall not be discharged into another dwelling unit.

    6. 6.Taking return air from a crawl space shall not be accomplished through a direct connection to the return side of a forced air furnace. Transfer openings in the crawl space enclosure shall not be prohibited.

    7. 7.Return air shall not be taken from a closet, bathroom, toilet room, kitchen, garage, boiler room, furnace room or unconditioned attic.

    Exceptions:

    1. 1.Taking return air from a kitchen is not prohibited where such return air openings serve the kitchen and are located not less than 10 feet (3048 mm) from the cooking appliances.

    2. 2.Dedicated forced air systems serving only the garage shall not be prohibited from obtaining return air from the garage.