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Wrong - The IRC prohibits the use of flex duct for kitchen exhaust and only permits PVC duct for downdraft systems that meet specific exceptions; also, gaps at the ceiling have not been air sealed.

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This exhaust fan duct opens into the attic rather than exiting through the roof and mold has begun to form on the underside of the deck sheathing and on the rafter due to the moist air exiting the duct

This exhaust fan duct opens into the attic rather than exiting through the roof and mold has begun to form on the underside of the deck sheathing and on the rafter due to the moist air exiting the duct

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Exhaust fan ducts should be made of rigid metal ducting not flexible corrugated ducts like these and the ducts should be attached to the roof or soffit to vent completely to the outside not left open in the attic near an attic vent

Exhaust fan ducts should be made of rigid metal ducting not flexible corrugated ducts like these and the ducts should be attached to the roof or soffit to vent completely to the outside not left open in the attic near an attic vent

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Kitchen Exhaust Retrofit Duct Guide

Guide

Guide describing the retrofit of kitchen exhaust systems, including duct sizing and routing considerations.

Duct Leakage Testing for Central Exhaust and Ventilation Systems in Multifamily Buildings

Guide

Guide describing the testing of duct leakage in central ventilation systems for multi-story, multi-family buildings.