506.3 Ducts Serving Type I Hoods
Grease ducts serving Type I hoods 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.
- Penetrations shall not be required to be welded or brazed where sealed by devices that are listed for the application.
- 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.
- Factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978 and installed in accordance with Section 304.1.
Exceptions: This section shall not apply to:
- 1.1. The hood duct opening 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.
- 1.2. The 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 duct not less than 1 inch (25 mm) above the bottom end of the duct.
- 1.3. A gasket rated for use at not less than 1500°F (816°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 (102 mm) on center for the full perimeter of the opening. The bolts and nuts shall be secured with lockwashers.
- Listed and labeled duct-to-hood collar connections installed in accordance with Section 304.1.
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 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 light test shall be performed by passing a lamp having a power rating of not less than 100 watts 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 test 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. For listed factory-built grease ducts, this test shall be limited to duct joints assembled in the field and shall exclude factory welds.
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 mm) in length and are designed to prevent the trapping of grease.
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).
- Factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978.
- Listed and labeled exhaust equipment installed in accordance with Section 304.1.
- 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.
Grease duct reservoirs shall:
- Be constructed as required for the grease duct they serve.
- Be located on the bottom of the horizontal duct or the bottommost section of the duct riser.
- Extend across the full width of the duct and have a length of not less than 12 inches (305 mm).
- Have a depth of not less than 1 inch (25 mm).
- Have a bottom that slopes to a drain.
- 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.
- Be installed in accordance with the manufacturer's instructions where manufactured devices are utilized.
Grease duct cleanouts and openings shall comply with all of the following:
- Grease ducts shall not have openings except where required for the operation and maintenance of the system.
- 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).
- Cleanouts and openings shall be equipped with tight-fitting doors constructed of steel having a thickness not less than that required for the duct.
- Cleanout doors shall be installed liquid tight.
- Door assemblies including any frames and gaskets shall be approved for the application and shall not have fasteners that penetrate the duct.
- Gasket and sealing materials shall be rated for not less than 1500°F (816°C).
- Listed door assemblies shall be installed in accordance with the manufacturer's instructions.
Cleanouts serving horizontal sections of grease ducts shall:
- Be spaced not more than 20 feet (6096 mm) apart.
- Be located not more than 10 feet (3048 mm) from changes in direction that are greater than 45 degrees (0.79 rad).
- 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.
- Not be closer than 1 inch (25 mm) from the edges of the duct.
- 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.
- Shall be located at grease reservoirs.
Underground grease duct installations shall comply with all of the following:
- 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).
- The underground duct system shall be tested and approved in accordance with Section 506.3.2.5 prior to coating or placement in the ground.
- The underground duct system shall be completely encased in concrete with a minimum thickness of 4 inches (102 mm).
- Ducts shall slope toward grease reservoirs.
- A grease reservoir with a cleanout to allow cleaning of the reservoir shall be provided at the base of each vertical duct riser.
- Cleanouts shall be provided with access to permit cleaning and inspection of the duct in accordance with Section 506.3.
- Cleanouts in horizontal ducts shall be installed on the topside of the duct.
- Cleanout locations shall be legibly identified at the point of access from the interior space.