Where domestic range hoods and domestic appliances equipped with downdraft exhaust are provided, such hoods and appliances shall discharge to the outdoors through sheet metal ducts constructed of galvanized steel, stainless steel, aluminum or copper. Such ducts shall have smooth inner walls, shall be air tight, shall be equipped with a backdraft damper, and shall be independent of all other exhaust systems.
- In other than Group I-1 and I-2, where installed in accordance with the manufacturer's instructions and where mechanical or natural ventilation is otherwise provided in accordance with Chapter 4, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.
- Ducts for domestic kitchen cooking appliances equipped with downdraft exhaust systems shall be permitted to be constructed of Schedule 40 PVC pipe and fittings provided that the installation complies with all of the following:
- The duct shall be installed under a concrete slab poured on grade.
- The underfloor trench in which the duct is installed shall be completely backfilled with sand or gravel.
- The PVC duct shall extend not more than 1 inch (25 mm) above the indoor concrete floor surface.
- The PVC duct shall extend not more than 1 inch (25 mm) above grade outside of the building.
- The PVC ducts shall be solvent cemented.
Exhaust hood systems capable of exhausting in excess of 400 cfm (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.
Where a common multistory duct system is designed and installed to convey exhaust from multiple domestic kitchen exhaust systems, the construction of the system shall be in accordance with all of the following:
- The shaft in which the duct is installed shall be constructed and fire-resistance rated as required by the International Building Code.
- Dampers shall be prohibited in the exhaust duct, except as specified in Section 505.1. Penetrations of the shaft and ductwork shall be protected in accordance with Section 607.5.5, Exception 2.
- Rigid metal ductwork shall be installed within the shaft to convey the exhaust. The ductwork shall be constructed of sheet steel having a minimum thickness of 0.0187 inch (0.4712 mm)(No. 26 gage) and in accordance with SMACNA Duct Construction Standards.
- The ductwork within the shaft shall be designed and installed without offsets.
- The exhaust fan motor design shall be in accordance with Section 503.2.
- The exhaust fan motor shall be located outside of the airstream.
- The exhaust fan shall run continuously, and shall be connected to a standby power source.
- Exhaust fan operation shall be monitored in an approved location and shall initiate an audible or visual signal when the fan is not in operation.
- Where the exhaust rate for an individual kitchen exceeds 400 cfm (0.19 m3/s) makeup air shall be provided in accordance with Section 505.2.
- A cleanout opening shall be located at the base of the shaft to provide access to the duct to allow for cleanout and inspection. The finished openings shall be not less than 12 inches by 12 inches (305 mm by 305 mm).
- Screens shall not be installed at the termination.
- The common multistory duct system shall serve only kitchen exhaust and shall be independent of other exhaust systems.