N.Y.C. Admin. Code § MC 506: Section MC 506: Commercial Kitchen Hood Ventilation System Ducts and Exhaust Equipment

506.1 General.

Commercial kitchen hood ventilation ducts and exhaust equipment shall comply with the requirements of this section. Commercial kitchen grease ducts shall be designed for the type of cooking appliance and hood served. All ducts shall lead directly to the exterior of the building and terminate as required by Section 506.3.13 for Type 1 hoods and Section 506.4.2 for Type II hoods.

Exception: Recirculating hoods that comply with Exception 2 of Section 507.1 do not require ducting in accordance with this section.

506.2 Corrosion protection.

Ducts exposed to the outside atmosphere or subject to a corrosive environment shall be protected against corrosion.

506.3 Ducts serving Type I hoods.

Type I exhaust ducts shall be independent of all other exhaust systems except as provided in Section 506.3.5. Commercial kitchen duct systems serving Type I hoods shall be designed, constructed and installed in accordance with Sections 506.3.1 through 506.3.13.3.

506.3.1 Duct materials.

Ducts serving Type I hoods shall be constructed of materials in accordance with Sections 506.3.1.1 and 506.3.1.2.

506.3.1.1 Grease duct materials.

Grease ducts serving Type I hoods, and located within buildings, shall be constructed as follows:

1. Ducts with a cross-sectional area up to and including 155 square inches (1.0 square meters) shall be constructed of 0.0598-inch (1.52 mm) No. 16 Gage steel;

2. Ducts with a cross-sectional area over 155 square inches (100 000 mm

2

), but not more than 200 square inches (0.129 m

2

) shall be constructed of 0.074-inch (1.9 mm) No. 14 Gage steel; and

3. Ducts with a cross-sectional area equal to or more than 200 square inches (0.129 m

2

) shall be constructed of 0.1046-inch (2.66 mm) No. 12 Gage steel.

If stainless steel is used for ducts of any of the cross-sectional areas listed above, the Gage steel may be increased upwards (resulting in a smaller thickness) by 1 even Gage size.

Exception: Listed and labeled factory-built commercial kitchen grease ducts shall be listed and labeled in accordance with UL 1978 and installed in accordance with Section 304.1 and as approved by the commissioner.

506.3.1.2 Makeup air ducts.

Makeup air ducts connecting to or within 18 inches (457.2 mm) of a Type I hood shall be constructed and installed in accordance with Sections 603.1, 603.3, 603.4, 603.9, 603.10, and 603.12. Duct insulation installed within 18 inches (457.2 mm) of a Type I hood shall be noncombustible or shall be listed for the application.

506.3.2 Joints, seams and penetrations of grease ducts.

Joints, seams and penetrations of grease ducts shall be made with a continuous liquid-tight weld or braze made on the external surface of the duct system.

Exceptions:

1. Penetrations shall not be required to be welded or brazed where sealed by devices that are listed for the application.

2. Internal welding or brazing shall not be prohibited provided that the joint is formed or ground smooth and is provided with ready access for inspection.

3. Factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978 and installed in accordance with Section 304.1 of this code.

506.3.2.1 Duct joint types.

Duct joints shall be butt joints, welded flange joints with a maximum flange depth of 1/2 inch (12.7 mm) or overlapping duct joints of either the telescoping or bell type. Overlapping joints shall be installed to prevent ledges and obstructions from collecting grease or interfering with gravity drainage to the intended collection point. The difference between the inside cross-sectional dimensions of overlapping sections of duct shall not exceed 1/4 inch (6.4 mm). The length of overlap for overlapping duct joints shall not exceed 2 inches (50.8 mm).

506.3.2.2 Duct-to-hood joints.

Duct-to-hood joints shall be made with continuous internal or external liquid-tight welded or brazed joints. Such joints shall be smooth, accessible for inspection, and without grease traps.

Exceptions: This section shall not apply to:

1. A vertical duct-to-hood collar connection made in the top plane of the hood in accordance with all of the following:

1.1. The hood duct opening shall have a 1-inch-deep (25.4 mm), full perimeter, welded flange turned down into the hood interior at an angle of 90 degrees (1.57 rad) from the plane of the opening.

1.2. The duct shall have a 1-inch-deep (25.4 mm) flange made by a 1-inch by 1-inch (25.4 mm by 25.4 mm) angle iron welded to the full perimeter of the duct not less than 1 inch (25.4 mm) above the bottom end of the duct.

1.3. A gasket rated for use at not less than 1,500°F (815.6°C) is installed between the duct flange and the top of the hood.

1.4. The duct-to-hood joint shall be secured by stud bolts not less than 1/4 inch (6.4 mm) in diameter welded to the hood with a spacing not greater than 4 inches (101.6 mm) on center for the full perimeter of the opening. The bolts and nuts shall be secured with lockwashers.

2. Listed and labeled duct-to-hood collar connections installed in accordance with Section 304.1.

506.3.2.3 Duct-to-exhaust fan connections.

Duct-to-exhaust fan connections shall be flanged and gasketed at the base of the fan for vertical discharge fans; shall be flanged, gasketed and bolted to the inlet of the fan for side-inlet utility fans; and shall be flanged, gasketed and bolted to the inlet and outlet of the fan for in-line fans. Approved flexible connectors may be provided. Gasket and sealing materials shall be rated for continuous duty at a temperature of not less than 1,500ºF (815.6ºC).

506.3.2.4 Vibration isolation.

A vibration isolation connector for connecting a duct to a fan shall consist of noncombustible packing in a metal sleeve joint of approved design or shall be a coated-fabric flexible duct connector listed and labeled for the application. Vibration isolation connectors shall be installed only at the connection of a duct to a fan inlet or outlet.

506.3.2.5 Grease duct test.

Prior to the use or concealment of any portion of a grease duct system, a leakage test shall be performed. Ducts shall be considered to be concealed where installed in shafts or covered by coatings or wraps that prevent the ductwork from being visually inspected on all sides. The duct installer shall be responsible for providing the necessary equipment and performing the grease duct leakage test. A duct leakage test, in accordance with this section, shall be performed for the entire duct system, including the hood-to-duct connection. The duct work shall be permitted to be tested in sections, provided that every joint is tested.

To determine the tightness of the grease duct construction, a smoke test shall be made in accordance with the following conditions and requirements:

1. The test shall be performed in the presence of the special inspector.

2. The grease duct shall be filled with a thick penetrating smoke produced by one or more smoke machines, or smoke bombs. A static pressure equal to or not less than 2" wg shall be maintained throughout the test. The test shall be applied for a length of time sufficient to permit the inspection of the grease duct.

3. If the test shows any evidence of leakage or other defects, such defects shall be corrected in accordance with the requirements of this chapter, and the test shall be repeated until there is no visible smoke observed.

506.3.3 Grease duct supports.

Grease duct bracing and supports shall be of noncombustible material securely attached to the structure and designed to carry gravity and seismic loads within the stress limitations of the New York City Building Code. Bolts, screws, rivets and other mechanical fasteners shall not penetrate duct walls.

506.3.4 Air velocity.

Grease duct systems serving a Type I hood shall be designed and installed to provide an air velocity within the duct system of not less than 500 feet per minute (2.5 m/s).

Exception: The velocity limitations shall not apply within duct transitions utilized to connect ducts to differently sized or shaped openings in hoods and fans, provided that such transitions do not exceed 3 feet (914.4 mm) in length and are designed to prevent the trapping of grease.

506.3.5 Separation of grease duct system.

A separate grease duct system shall be provided for each Type I hood.

Exceptions:

1. A separate grease duct system is not required where all of the following conditions are met:

1.1. All interconnected hoods are located within the same story, provided that they are part of the same facility and under the control of one owner or tenant.

1.2. All interconnected hoods are located within the same room or in adjoining rooms, provided that they are part of the same facility and under the control of one owner or tenant.

1.3. Interconnecting ducts do not penetrate assemblies required to be fire-resistance rated.

1.4. The grease duct system does not serve solid fuel-fired appliances.

2. Branch ducts from other equipment in the same kitchen area, or from registers exhausting the kitchen space in general, may be connected to the main hood exhaust duct if the following requirements are complied with:

2.1. A fusible link fire damper of the same gage as the hood exhaust duct shall be added at the point of connection of the branch duct to the exhaust duct.

2.2. If the branch connection is made to the portion of the ductwork that will contain the fire-extinguishing medium, then the fire dampers required in Exception 2.1 shall be arranged to close automatically upon the operation of the fire-extinguishing system.

2.3. The branch connection shall be made in either the top or sides of the main duct in a manner to prevent grease from flowing into the branch duct.

2.4. The branch ducts shall be constructed of steel, aluminum, or copper of the gages and weights required in Chapter 6, and they shall be insulated with 2 inches (50.8 mm) of magnesia or other material having equivalent insulative and fire resistance qualities.

2.5. All registers in these branches shall have fusible link actuated dampers.

2.6. Where branch ductwork is to be used to exhaust vapors from dishwashers, pot sinks, or other similar equipment of a commercial type from which moisture is emitted, copper or aluminum of the minimum gage and weights required in Chapter 6 shall be used. Such ductwork shall be installed so that condensate cannot leak from it.

2.7 Type I and Type II exhaust systems can be interconnected downstream of filters with a fire damper at the connection to the exhaust system.

506.3.6 Grease duct clearances.

Where enclosures are not required, grease duct systems and exhaust equipment serving a Type I hood shall have a clearance to combustible construction of not less than 18 inches (457.2 mm), and shall have a clearance to noncombustible construction and gypsum wallboard attached to noncombustible structures of not less than 3 inches (76.2 mm).

Exceptions:

1. For factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978, the required clearance shall be in accordance with the listing of such material and as approved by the commissioner.

2. Listed and labeled exhaust equipment installed in accordance with Section 304.1.

3. Where commercial kitchen grease ducts are continuously covered on all sides with a listed and labeled field-applied grease duct enclosure material, system, product or method of construction specifically evaluated for such purpose in accordance with ASTM E 2336, the required clearance shall be in accordance with the listing of such material, system, product or method.

4. Grease ducts protected with a minimum insulation covering of 2 inches (50.8 mm) of magnesium or calcium silicate block, with staggered joints, attached with galvanized steel wire or material assembly equivalent in insulating and fire-resistant qualities which cannot be penetrated by grease. Such protection shall be applied to all ducts inside of the building as approved by the commissioner.

506.3.7 Prevention of grease accumulation in grease ducts.

Duct systems serving a Type I hood shall be constructed and installed so that grease cannot collect in any portion thereof, and the system shall slope not less than one-fourth unit vertical in 12 units horizontal (2-percent slope) toward the hood or toward a grease reservoir designed and installed in accordance with Section 506.3.7.1. Where horizontal ducts exceed 75 feet (22 860 mm) in length, the slope shall be not less than one unit vertical in 12 units horizontal (8.3-percent slope). Dampers shall not be installed in the grease duct systems, except as required by Section 506.3.5, Exception 2.

506.3.7.1 Grease duct reservoirs.

Grease duct reservoirs shall:

1. Be constructed as required for the grease duct they serve.

2. Be located on the bottom of the horizontal duct or the bottommost section of the duct riser.

3. Extend across the full width of the duct and have a length of not less than 12 inches (304.8 mm).

4. Have a depth of not less than 1 inch (25.4 mm).

5. Have a bottom that slopes to a capped drain connection.

6. Be provided with a cleanout opening constructed in accordance with Section 506.3.8 and installed to provide direct access to the reservoir. The cleanout opening shall be located on a side or on top of the duct so as to permit cleaning of the reservoir.

7. Be installed in accordance with the manufacturer's instructions where manufactured devices are utilized.

506.3.8 Grease duct cleanouts and other openings.

Grease duct systems shall not have openings therein other than those required for proper operation and maintenance of the system. Any portion of such system having sections not provided with access from the duct entry or discharge shall be provided with cleanout openings. Cleanout openings shall be provided at every change indirection, within 3 feet (914.4 mm) of the exhaust fan, and as required under Section 506.3.9. Cleanout openings shall be equipped with tight-fitting doors constructed of steel having a thickness not less than that required for the duct. Doors shall be equipped with a substantial method of latching, sufficient to hold the door tightly closed. Doors shall be designed so that they are operable without the use of a tool. Door assemblies shall have a gasket or sealant that is noncombustible and liquid tight, and shall not have fasteners that penetrate the duct. Listed and labeled access door assemblies shall be installed in accordance with the terms of the listing. Signage shall be provided at all required access doors and openings in accordance with Section 506.3.12.

506.3.8.1 Personnel entry.

Where ductwork is large enough to allow entry of personnel, not less than one approved or listed opening having dimensions not less than 22 inches by 20 inches (558.8 mm by 508 mm) shall be provided in the horizontal sections, and in the top of vertical risers. Where such entry is provided, the duct and its supports shall be capable of supporting the additional load and the cleanouts specified in Section 506.3.8 are not required. Where personnel entry is not possible for cleaning the interior of vertical ducts, suitable provisions shall be made to clean the vertical duct in its entirety as well as for cleaning the base of the vertical riser.

506.3.8.2 Cleanouts serving in-line fans.

A suitable cleanout shall be provided for both the inlet side and outlet side of an in-line fan except where a duct does not connect to the fan. Such cleanouts shall be located within 3 feet (914.4 mm) of the fan duct connections to permit a thorough cleaning of the inlet and discharge ducts connected to the in-line fan as well as the interior of the fan itself.

Exception: Where suitable cleanouts for in-line fans cannot be provided, the in-line fan shall be of "clam shell" construction which shall permit the fan to be opened and thoroughly cleaned while remaining in place.

506.3.9 Grease duct horizontal cleanouts.

Cleanouts located on horizontal sections of ducts shall be spaced not more than 20 feet (6096 mm) apart, unless the opening prescribed by Section 506.3.8.1 is not possible, in which case openings large enough to permit thorough cleaning shall be provided at 12-foot (3657.6 mm) intervals. The cleanouts shall be located on the side of the duct with the opening not less than 1.5 inches (38.1 mm) above the bottom of the duct, and not less than 1 inch (25.4 mm) below the top of the duct. The opening minimum dimensions shall be 12 inches (304.8 mm) on each side. Where the dimensions of the side of the duct prohibit the cleanout installation prescribed herein, the openings shall be on the top of the duct or the bottom of the duct. Where located on the top of the duct, the opening edges shall be a minimum of 1 inch (25.4 mm) from the edges of the duct. Where located in the bottom of the duct, cleanout openings shall be designed to provide internal damming around the opening, shall be provided with gasketing to preclude grease leakage, shall provide for drainage of grease down the duct around the dam and shall be approved for the application. Where the dimensions of the sides, top or bottom of the duct preclude the installation of the prescribed minimum-size cleanout opening, the cleanout shall be located on the duct face that affords the largest opening dimension and shall be installed with the opening edges at the prescribed distances from the duct edges as previously set forth in this section.

506.3.10 Underground and raised floor cavity grease duct installation.

Grease ducts shall not be installed underground or in raised floor cavities.

506.3.11 Grease duct enclosure.

A commercial kitchen grease duct serving a Type I hood that penetrates a ceiling, wall, floor or any concealed space shall be enclosed from the first point of penetration to the outlet terminal. In-line exhaust fans not located outdoors shall be enclosed as required for grease ducts. A duct shall penetrate exterior walls only at locations where unprotected openings are permitted by the New York City Building Code. The duct enclosure shall serve a single grease duct and shall not contain other ducts, piping or wiring systems. Duct enclosures shall be a shaft enclosure in accordance with Section 506.3.11.1, a field-applied enclosure assembly in accordance with Section 506.3.11.2 or a factory-built enclosure assembly in accordance with Section 506.3.11.3. Duct enclosures shall have a fire-resistance rating of not less than that of the fire-resistance-rated assembly penetrated and not less than 1 hour. Fire dampers and smoke dampers shall not be installed in grease ducts.

Exception: A duct enclosure shall not be required for a grease duct that penetrates only a nonfire-resistance-rated roof/ceiling assembly.

506.3.11.1 Shaft enclosure.

Grease ducts constructed in accordance with Section 506.3.1 shall be permitted to be enclosed in accordance with the New York City Building Code requirements for shaft construction. Such grease duct systems and exhaust equipment shall have a clearance to combustible construction of not less than 18 inches (457.2 mm), and shall have a clearance to noncombustible construction and gypsum wallboard attached to noncombustible structures of not less than 6 inches (152.4 mm). Duct enclosures shall be sealed around the duct at the point of penetration and vented to the outside of the building through the use of weather-protected openings.

Exceptions:

1. The shaft enclosure provisions of this section shall not be required where a duct penetration is protected with a through-penetration firestop system classified in accordance with ASTM E 814 and having an "F" and "T" rating equal to the fire-resistance rating of the assembly being penetrated and where the surface of the duct is continuously covered on all sides from the point at which the duct penetrates a ceiling, wall or floor to the outlet terminal with a classified and labeled material, system, method of construction or product specifically evaluated for such purpose, which material, system, method of construction or product is approved by the commissioner and installed according to the manufacturer's instructions. Exposed duct wrap systems shall be protected where subject to physical damage.

2. As an alternative to Exception 1 of this section, a minimum insulation covering of 2 inches (50.8 mm) of magnesium or calcium silicate block, with staggered joints, attached with galvanized steel wire or material assembly equivalent in insulating and fire-resistant qualities which cannot be penetrated by grease, and as approved by the commissioner, shall be applied to all ducts inside of the building.

3. A duct enclosure shall not be required for a grease duct that penetrates only a nonfire-resistance-rated roof/ceiling assembly.

4. A listed and labeled factory-built commercial kitchen grease duct system, evaluated as an enclosure system for reduced clearances to combustibles, and approved by the commissioner and installed according to manufacturer's instructions.

506.3.11.2 Field-applied grease duct enclosure.

Grease ducts constructed in accordance with Section 506.3.1 shall be enclosed by a listed and labeled field-applied grease duct enclosure material, systems, product, or method of construction specifically evaluated for such purpose in accordance with ASTM E 2336. The surface of the duct shall be continuously covered on all sides from the point at which the duct originates to the outlet terminal. Duct penetrations shall be protected with a through-penetration firestop system tested and listed in accordance with ASTM E 814 or UL 1479 and having an "F" and "T" rating equal to the fire-resistance rating of the assembly being penetrated. The grease duct enclosure and firestop system shall be installed in accordance with the listing and the manufacturer's instructions. Exposed duct-wrap systems shall be protected where subject to physical damage.

506.3.11.3 Factory-built grease duct enclosure assemblies.

Factory-built grease ducts incorporating integral enclosure materials shall be listed and labeled for use as grease duct enclosure assemblies specifically evaluated for such purpose in accordance with UL 2221. Duct penetrations shall be protected with a through-penetration firestop system tested and listed in accordance with ASTM E 814 or UL 1479 and having an "F" and "T" rating equal to the fire-resistance rating of the assembly being penetrated. The grease duct enclosure assembly and firestop system shall be installed in accordance with the listing and the manufacturer's instructions.

506.3.12 Grease duct fire-resistive access opening.

Where cleanout openings are located in ducts within a fire-resistance-rated enclosure, access openings shall be provided in the enclosure at each cleanout point. Access openings shall be equipped with tight-fitting sliding or hinged doors that are equal in fire-resistive protection to that of the shaft or enclosure. An approved sign shall be placed on access opening panels with wording as follows: "ACCESS PANEL. DO NOT OBSTRUCT." Cleanout openings provided in ducts that are not located within a fire-resistance-rated enclosure shall be provided with signage at the required opening that contains the same wording.

506.3.13 Exhaust outlets serving Type I hoods.

Exhaust outlets for grease ducts serving Type I hoods shall conform to the requirements of Sections 506.3.13.1 through 506.3.13.3.

506.3.13.1 Termination above the roof.

Exhaust outlets that terminate above the roof shall have the discharge opening located not less than 40 inches (1016 mm) above the roof surface. The exhaust flow shall be directed away from the surface of the roof.

506.3.13.2 Termination through an exterior wall.

Exhaust outlets shall be permitted to terminate through exterior walls where the smoke, grease, gases, vapors and odors in the discharge from such terminations do not create a public nuisance or a fire hazard. Such terminations shall not be located where protected openings are required by the New York City Building Code. Other exterior openings shall not be located within 3 feet (914.4 mm) of such terminations.

506.3.13.3 Termination location.

Exhaust outlets shall be located not less than 10 feet (3048 mm) horizontally from parts of the same or contiguous buildings, adjacent buildings and adjacent property lines and shall be located not less than 10 feet (3048 mm) above the adjoining grade level. Exhaust outlets shall be located not less than 10 feet (3048 mm) horizontally from and not less than 3 feet (914.4 mm) above air intake openings into any building.

Exception: Exhaust outlets shall terminate not less than 5 feet (1524 mm) horizontally from parts of the same or contiguous building, an adjacent building, adjacent property line and air intake openings into a building where air from the exhaust outlet discharges away from such locations.

506.4 Ducts serving Type II hoods.

Commercial kitchen exhaust systems serving Type II hoods shall comply with Sections 506.4.1 and 506.4.2.

506.4.1 Ducts.

Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials. Duct construction, installation, bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure and ducts conveying moisture-laden or waste-heat-laden air shall be constructed, joined and sealed in an approved manner.

506.4.2 Type II terminations.

Exhaust outlets serving Type II hoods shall terminate in accordance with the hood manufacturer's instructions and shall comply with all of the following:

1. Outlets shall terminate not less than 3 feet (914.4 mm) in any direction from openings into the building.

2. Outlets shall terminate not less than 10 feet (3048 mm) from property lines or buildings on the same lot.

3. Outlets shall terminate not less than 10 feet (3048 mm) above grade.

4. Outlets that terminate above a roof shall terminate not less than 30 inches (762 mm) above the roof's surface.

5. Outlets shall terminate not less than 30 inches (762 mm) from exterior vertical walls.

6. Outlets shall be protected against local weather conditions.

7. Outlets shall not be directed onto walkways.

8. Outlets shall meet the provisions for exterior wall opening protectives in accordance with the New York City Building Code.

506.4.2.1 Cooking spaces.

For all buildings other than those classified as residential occupancy, a minimum of No. 16 Gage for galvanized sheet duct shall be used for nongrease duct exhaust applications.

506.5 Exhaust equipment.

Exhaust equipment, including fans and grease reservoirs, shall comply with Section 506.5.1through 506.5.5 and shall be of an approved design or shall be listed for the application.

506.5.1 Exhaust fans.

Exhaust fan housings serving a Type I hood shall be constructed as required for grease ducts in accordance with Section 506.3.1.1.

Exception: Fans listed and labeled in accordance with UL 762.

506.5.1.1 Fan motor.

Exhaust fan motors shall be located outside of the exhaust airstream.

506.5.1.2 In-line fan location.

Where enclosed duct systems are connected to in-line fans not located outdoors, the fan shall be located in a room or enclosure having the same fire-resistance rating as the duct enclosure. Access shall be provided for servicing and cleaning of fan components. Such rooms or enclosures shall be ventilated in accordance with the fan manufacturer's instructions.

506.5.2 Exhaust fan discharge.

Exhaust fans shall be positioned so that the discharge will not impinge on the roof, other equipment or appliances or parts of the structure. A vertical discharge fan serving a Type 1 hood shall be manufactured with an approved drain outlet at the lowest point of the housing to permit drainage of grease to an approved grease reservoir.

506.5.3 Exhaust fan mounting.

Up-blast fans serving Type I hoods and installed in a vertical or horizontal position shall be hinged, supplied with a flexible weatherproof electrical cable to permit inspection and cleaning and shall be equipped with a means of restraint to limit the swing of the fan on its hinge. The ductwork shall extend not less than 18 inches (457.2 mm) above the roof surface.

506.5.4 Reserved.

506.5.5 Termination location.

The outlet of exhaust equipment serving Type I hoods, shall be in accordance with Section 506.3.13.

Exception: The minimum horizontal distance between vertical discharge fans and parapet-type building structures shall be 2 feet (609.6 mm) provided that such structures are not higher than the top of the fan discharge opening.

506.5.6 Exhaust fan operation.

The operation of the exhaust fan shall be in accordance with the following requirements:

1. The hood exhaust fan(s) shall continue to operate after the extinguishing system has been activated unless fan shutdown is required by a listed component of the ventilation system or by the design of the extinguishing system.

2. The hood exhaust fan shall not be required to start automatically upon activation of the extinguishing system if the exhaust fan and all cooking equipment served by the fan have previously been shut down.

3. The cooking appliances shall be interlocked with the exhaust hood system to prevent appliance operation when the exhaust hood system is not operating.

506.6 Exterior duct installations.

The installation of exterior ducts shall comply with the following requirements:

1. The exterior portion of the ductwork shall be vertical wherever possible and shall be installed and supported on the exterior of a building.

2. Bolts, screws, rivets, and other mechanical fasteners shall not penetrate duct walls.

3. Clearance of any ducts shall comply with Section 506.3.6.

4. All ducts shall be protected on the exterior by paint or other suitable weather-protective coating.

5. Ducts constructed of stainless steel shall not be required to have additional paint or weather-protective coatings.

6. Ductwork subject to corrosion shall have minimal contact with the building surface.

7. No portion of an exterior metal duct shall be nearer than 24 inches (609.6 mm) to any door or window or to any exit, or located where it would be readily accessible to the public, unless it is insulated or shielded to avoid injury to any person coming in contact with the duct.

Exception: Listed and labeled factory-built commercial kitchen grease ducts may be used when installed in accordance with Section 304.1.

506.7 Identification of ducts.

All duct systems serving Type I and Type II exhaust equipment shall be permanently labeled: "CAUTION: KITCHEN EXHAUST SYSTEM." At the base of each duct and at its termination point, a clearly identifiable permanent sign shall be installed identifying the facility from which the duct originates.