Here’s what NFPA 96 has to say about balancing dampers in commercial kitchen exhaust ducts.
Chapter 9 Auxiliary Equipment
9.1.1 Dampers shall not be installed in exhaust ducts or exhaust duct systems.
9.1.2 Where specifically listed for such use or where required as part of a listed device or system, dampers in exhaust ducts or exhaust duct systems shall be permitted.
A common misperception is that dampers are not allowed in grease ducts. That is not the case, grease ducts ARE allowed IF specifically listed for such use. The Authority Having Jurisdiction (AHJ) has the final say and local codes should be a reference to confirm their acceptance. There is a specific approval for New York City (COA, Certificate of Acceptance) that is required. Confirm the damper you are contemplating using has such approval.
Dampers that carry this listing may be automated, balancing type, such as those associated with demand control ventilation systems. These dampers are designed to continually modulate exhaust air volume (i.e. model ABD) or a manual type (i.e. model MBD) for setting the volume of individual hoods connected to a common exhaust duct system. If permitted by their listing, such dampers may be factory-installed on the duct collar of the hood(s) or field-installed remotely in the branch exhaust duct of the hood that it is serving. This is typically done when there is an issue with overhead height clearance.
Automated dampers that are installed on a common duct system with multiple hoods connected have been proven to increase the savings that may be realized by the use of a demand control ventilation system by as much as 50% over non-damper systems.
Manual dampers provide an accurate method of balancing the exhaust air volumes of multiple hood sections operating on a common duct and fan system for constant volume systems.
Regional Sales Manager, Halton Canada
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Read our related article, Demand Control Ventilation Systems for Commercial Kitchens, how do they differ, how are they the same?
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