Free Technical Information for Building Inspectors, Contractors and Consumers. Code and Manufacturer's Information Resource
Ranges- Downdraft Vents
1. Jenn-Aire Electric Down-Draft Installation Guide: Guide
2. For Electrolux : Electrolux-USA
What does the Code Say?
M1502
RANGE HOODS
M1502.1 General.
Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight and shall be equipped with a backdraft damper. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.
Exception: Where installed in accordance with the manufacturer's installation instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.
M1502.2 Duct material.
Single-wall ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper.
Exception: Ducts for domestic kitchen cooking appliances equipped with downdraft exhaust systems shall be permitted to be constructed of schedule 40 PVC pipe provided that the installation complies with all of the following:
1. The duct shall be installed under a concrete slab poured on grade,
2. The underfloor trench in which the duct is installed shall be completely backfilled with sand or gravel,
3. The PVC duct shall extend not greater than 1 inch (25.4 mm) above the indoor concrete floor surface,
4. The PVC duct shall extend not greater than 1 inch (25.4 mm) above grade outside of the building, and 5. The PVC ducts shall be solvent cemented.
M1502.3 Kitchen exhaust rates.
Where domestic kitchen cooking appliances are equipped with ducted range hoods or down-draft exhaust systems, the fans shall be sized in accordancewithSectionM1506.3.
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Down-Draft Units:
• Best performance is achieved by using round duct instead of rectangular, especially when elbows are required.
• If multiple elbows are needed, ensure that there is a minimum of 24” of straight duct between any two elbows.
• Avoid “S” or “back to back” configurations caused by adjacent elbows.
• Thermal breaks, such as a short section of non-metallic duct, should be used in areas of extreme cold.
• A back-draft damper at the duct outlet may also be required.
• Do not use flexible metal duct.
• Do not use duct work that is smaller in cross-sectional area than the recommended size duct.
• Do not rely on duct tape alone to seal duct joints. Use sheet metal screws as require to support the duct weight.
• The vent hood and cooking appliance(s) must be removable if service is required.
• Be certain that the duct work does not interfere with floor joists or wall studs.
• It is important to keep a minimum number of turns in the duct run, and to keep therun as short as possible.
• Do not restrict the air flow by reducing the duct cross-sectional areas when making hard joints or squeezing through a tight area.
• With concrete slab construction, “box-in” the duct work to prevent it fromcollapsing when the wet concrete is poured. Also allow room for electrical conduit.
• Cross-drafts or air currents caused by adjacent open windows or doors, HVAC outlets, and ceiling fans reduce vent efficiency.
