Thermador VCIN42GWS Installation Instructions - Page 10
Ductwork preparation
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Ductwork preparation Discharge direction The exhaust air is discharged upwards through a duct or directly through the outside wall into the open. Ducting recommendations Proper performance is dependent upon proper ducting. Local building codes may require the use of make-up air systems when using ducted ventilation systems greater than specified cubic feet per minute (CFM) of air movement. The specified CFM varies from locale to locale. It is the responsibility of the owner and the installer to determine if additional requirements and/or standards apply to specific installations. DO NOT USE FLEXIBLE DUCT; it creates back pressure/ air turbulence and reduces performance. Always install a metal vent cover where the ductwork exits the house. Hood must be vented to the outside of building only. COLD WEATHER installations should have an additional backdraft damper installed to minimize backward cold air flow and a nonmetallic thermal break to minimize conduction of outside temperatures as part of the ductwork. The damper should be on the cold air side of the thermal break. The break should be as close as possible to where the ducting enters the heated portion of the house. MAKE-UP AIR: Local building codes may require the use of make-up air systems when using ducted ventilation systems greater than specified CFM of air movement. The specified CFM varies from locale to locale. It is the responsibility of the owner and the installer to determine if additional requirements and/or standards apply to specific installations. To reduce risk of fire and to properly exhaust air, be sure to duct air outside. Do not vent exhaust air in spaces with walls or ceilings or into attics, crawl spaces or garages. The unit cannot be used in conjunction with a recirculation unit. Thermador recommends not exceeding 50 ft (15.24 m) equivalent of duct. Keep duct runs as short and straight as possible. Elbows and transitions fittings reduce air flow efficiency. Back to back elbows and "S" turns give very poor delivery and are not recommended. A short, straight length of duct at the inlet of a remote blower gives the best delivery. Hoods are supplied with a 10" (254 mm) transition. A locally supplied transition is required for other sizes. Use the "Equivalent Duct Lengths for Commonly Used Transitions" table to compute permissible lengths for duct runs to outdoors. Page. 10