Section 506 Commercial Kitchen Hood Ventilation System Ducts and Exhaust Equipment

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.

Ducts and exhaust equipment exposed to the outside atmosphere or subject to a corrosive environment shall be protected against corrosion in an approved manner.

Grease duct systems shall be designed, constructed and installed in accordance with Sections 506.3.1 through 506.3.13.3.

Grease ducts shall be constructed of steel having a minimum thickness of 0.0575 inch (1.463 mm) (No. 16 gage) or stainless steel not less than 0.0450 inch (1.14 mm) (No. 18 gage) in thickness.

Exception: Factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978 and installed in accordance with Section 304.1.

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 grease duct system.

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.

Grease 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 (51 mm).

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

1. A vertical duct-to-hood collar connection made in the top plane of the hood in accordance with all of the following:
   1. The exhaust outlet of the hood shall have a 1-inch-deep (25 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.
   2. The grease duct shall have a 1-inch-deep (25 mm) flange made by a 1-inch by 1-inch (25 mm by 25 mm) angle iron welded to the full perimeter of the grease duct not less than 1 inch (25 mm) above the bottom end of the duct.
   3. A gasket rated for use at not less than 1,500°F (816°C) is installed between the grease duct flange and the top of the hood.
   4. The grease 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 (102 mm) on center for the full perimeter of the opening. The bolts and nuts shall be secured with lockwashers.
   506.3.2.3 Grease Duct-to-Exhaust Fan Connections

   Grease 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. Gasket and sealing materials shall be rated for continuous duty at a temperature of not less than 1,500°F (816°C).

   506.3.2.4 Vibration Isolation

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

   506.3.2.5 Grease Duct Test

   A field test shall be performed prior to the use or concealment of any portion of a grease duct system. Grease ducts shall be considered to be concealed where installed in shafts or covered by coatings or wraps that prevent the grease ducts from being visually inspected on all sides. The permit holder shall be responsible to provide the necessary equipment and perform the grease duct leakage test. A light test shall be performed to determine that all welded and brazed joints are liquid tight.

   A test shall be performed for the entire grease duct system, including the hood-to-duct connection. The grease duct system shall be permitted to be tested in sections, provided that every joint is tested. For listed factory-built grease ducts, this test shall be limited to duct joints assembled in the field and shall exclude factory welds. The test shall be performed in accordance with either Section 506.3.2.5.1 or 506.3.2.5.2.

   506.3.2.5.1 Light Test

   A duct test shall be performed by passing a lamp, having not less than 1600 lumens, through the entire section of ductwork to be tested. The lamp shall be open so as to emit light equally in all directions perpendicular to the duct walls. A successful test shall be where the light from the lamp is not visible at any point on the exterior of the duct.

   506.3.2.5.2 Water Spray Test

   A duct test shall be performed by simulating a cleaning operation of the interior of the duct. A water pump capable of a flowing outlet pressure of not less than 1,200 psi (8274 kPa) shall be used, along with any necessary hoses and spray nozzles, to apply high-pressure water to the inside surfaces of the duct. A successful test shall be where there is no evidence of cleaning water at any point on the exterior of the duct.

   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 International Building Code. Bolts, screws, rivets and other mechanical fasteners shall not penetrate grease duct walls.

   506.3.4 Air Velocity

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

   Exception: The velocity limitations shall not apply within grease duct transitions utilized to connect grease ducts to differently sized or shaped openings in hoods and fans, provided that such transitions do not exceed 3 feet (914 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. A separate grease duct system is not required where all of the following conditions are met:

   1. All interconnected hoods are located within the same story.
   2. All interconnected hoods are located within the same room or in adjoining rooms.
   3. Interconnecting grease ducts do not penetrate assemblies required to be fire-resistance rated.
   4. The grease duct system does not serve solid-fuel-fired appliances .
   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 mm), and shall have a clearance to noncombustible construction and gypsum wallboard attached to noncombustible structures of not less than 3 inches (76 mm).

   Exceptions:
   1. Factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978.
   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 E2336, the required clearance shall be in accordance with the listing of such material, system, product or method.
   506.3.7 Prevention of Grease Accumulation in Grease Ducts

   Grease 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 1 /₄ 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 grease ducts exceed 75 feet (22 860 mm) in length, the slope shall be not less than 1 unit vertical in 12 units horizontal (8.3-percent slope).

   Exception: Factory-built grease ducts shall be installed at a slope that is in accordance with the listing and manufacturer's installation instructions.

   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 grease duct or the bottommost section of the grease duct riser.
   3. Extend across the full width of the grease duct and have a length of not less than 12 inches (305 mm).
   4. Have a depth of not less than 1 inch (25 mm).
   5. Have a bottom that slopes to a drain.
   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 grease 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 Openings Grease duct cleanouts and openings shall comply with all of the following:
   1. Grease ducts shall not have openings except where required for the operation and maintenance of the system.
   2. Sections of grease ducts that are inaccessible from the hood or discharge openings shall be provided with cleanout openings spaced not more than 20 feet (6096 mm) apart and not more than 10 feet (3048 mm) from changes in direction greater than 45 degrees (0.79 rad).
   3. Cleanouts and openings shall be equipped with tight-fitting doors constructed of steel having a thickness not less than that required for the grease duct.
   4. Cleanout doors shall be installed liquid tight.
   5. Door assemblies including any frames and gaskets shall be approved for the application and shall not have fasteners that penetrate the grease duct.
   6. Gasket and sealing materials shall be rated for not less than 1,500°F (816°C).
   7. Listed door assemblies shall be installed in accordance with the manufacturer's instructions.
   506.3.8.1 Personnel Entry

   Where a grease duct 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 (559 mm by 508 mm) shall be provided in the horizontal sections, and in the top of vertical risers. Where such entry is provided, the grease duct and its supports shall be capable of supporting the additional load, and the cleanouts specified in Section 506.3.8 are not required.

   506.3.8.2 Cleanouts Serving In-Line Fans

   A cleanout shall be provided for both the inlet side and outlet side of an in-line fan except where a grease duct does not connect to the fan. Such cleanouts shall be located within 3 feet (914 mm) of the fan duct connections.

   506.3.9 Grease Duct Horizontal Cleanouts Cleanouts serving horizontal sections of grease ducts shall:
   1. Be spaced not more than 20 feet (6096 mm) apart.
   2. Be located not more than 10 feet (3048 mm) from changes in direction that are greater than 45 degrees (0.79 rad).
   3. Be located on the bottom only where other locations are not available and shall be provided with internal damming of the opening such that grease will flow past the opening without pooling. Bottom cleanouts and openings shall be approved for the application and installed liquid tight.
   4. Not be closer than 1 inch (25 mm) from the edges of the grease duct.
   5. Have opening dimensions of not less than 12 inches by 12 inches (305 mm by 305 mm). Where such dimensions preclude installation, the opening shall be not less than 12 inches (305 mm) on one side and shall be large enough to provide access for cleaning and maintenance.
   6. Be located at grease reservoirs.
   7. Be located within 3 feet (914 mm) of horizontal discharge fans.
   506.3.10 Underground Grease Duct Installation Underground grease duct installations shall comply with all of the following:
   1. Underground grease ducts shall be constructed of steel having a minimum thickness of 0.0575 inch (1.463 mm) (No. 16 gage) and shall be coated to provide protection from corrosion or shall be constructed of stainless steel having a minimum thickness of 0.0450 inch (1.140 mm) (No. 18 gage).
   2. The underground grease duct system shall be tested and approved in accordance with Section 506.3.2.5 prior to coating or placement in the ground.
   3. The underground grease duct system shall be completely encased in concrete with a minimum thickness of 4 inches (102 mm).
   4. Ducts shall slope toward grease reservoirs.
   5. A grease reservoir with a cleanout to allow cleaning of the reservoir shall be provided at the base of each vertical grease duct riser.
   6. Cleanouts shall be provided with access to permit cleaning and inspection of the grease duct in accordance with Section 506.3.
   7. Cleanouts in horizontal grease ducts shall be installed on the topside of the grease duct.
   8. Cleanout locations shall be legibly identified at the point of access from the interior space.