3
DUCT DESIGN
3.10 Bathroom Exhausts and Vents
Flexible air ducts and air connectors listed and labeled in accordance to UL 181 are required to pass UL 181 Section 13 Mold Growth and Humidity Test. This test ensures that materials in air ducts are resistant to high humidity conditions and that mold introduced to the duct surface will not grow or spread. This testing requirement along with proper installation will allow flexible air ducts and connectors to be used in bathrooms as well as other high humidity applications or applications with the potential for mold growth.
Ducts used for exhausting bathrooms and vents in cold weather climate zones shall be insulated in order to avoid issues with condensation collecting on the inside surface of the ducts.
3.11 Deeply Buried Duct
The Air Duct Council is aware that certain local, state, and national building codes allow for the practice of encapsulating ducts within additional insulation materials. Additionally the codes allow for partially or deeply burying ducts under blown - in insulation when installed in attics. Although this can be considered an energy efficient method for improving the overall thermal performance of the system, encapsulating or burying ducts that already contain an outer vapor barrier can potentially lead to moisture problems when the ducts are installed in areas of the country conducive to condensation such as ASHRAE Climate Zones 1A, 2A, and 3A. In addition, encapsulating flexible ducts may invalidate the manufacturers listing to the UL181 Standard and/or the warranty. Care should be taken when considering the practice of encapsulating or burying a flexible duct system in this manner.
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Figure 7
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