Where domestic range hoods and domestic appliances equipped with downdraft exhaust are located within dwelling units, such hoods and appliances shall discharge to the outdoors through ducts constructed of galvanized steel, stainless steel, aluminum or copper. Such ducts shall have smooth inner walls and shall be air tight and equipped with a backdraft damper. Such exhaust system shall be installed in strict compliance with the manufacturer's recommendations as well as the requirements of the listing.
- Where installed in accordance with the manufacturer's installation 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 greater than 1 inch (25 mm) above the indoor concrete floor surface.
- The PVC duct shall extend not greater 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 in accordance with Table 403.3. 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.