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INSPECTION & INSTALLATION INSPECTION & INSTALLATION
4.9.2 Ducts in Crawl Spaces
In accordance with the building codes, ducts installed under a building structure shall not be in contact with the ground. All duct surfaces shall be at least 4” above the earth (i.e. not sitting directly on dirt, rocks etc.). In addition, the crawl space shall shield the ducting from environment exposure. For installations where the duct may be exposed, such as a mobile home crossover duct, only ducts designed and intended for use under exposed conditions shall be used. Care must also be taken to ensure that the area under the structure is free from potential flooding. Flexible duct vapor barriers offer protection to the insulation from normal moisture vapor transfer; however, ducts sitting in standing water from flooding will deteriorate and not perform as designed.
4.9.3 Ducts in Walls and Between Floors
Flexible air ducts can be installed in walls and between floors. When installed vertically in walls the ducts shall be supported by straps at six (6) feet maximum intervals (Refer to Section 4.5 Supporting Flexible Ducts). For exterior walls refer to the appropriate energy code for the minimum insulation required between the ducts and the exterior space.
4.9.4 Ducts in Plenums
The building codes require that materials installed in plenums have a Flame Spread Index of 25 or less and a Smoke Developed Index of 50 or less when tested in accordance with ASTM E84. All listed and labeled Class 1 or Class 0 Flexible Air Ducts and Air Connectors meet this requirement and therefore may be installed within a plenum.
4.9.5 Ducts in Fire Resistant Rated Assemblies
Refer to Section 3.7 for materials allowed in Fire Resistant Rated Assemblies.
4.9.6 Ducts Exposed to the Elements
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Unless specifically designed and labeled for outdoor use, flexible air ducts and air connectors shall not be used outdoors. Refer to the appropriate energy code for specific duct insulation requirements when ducts are installed outdoors.
4.10 Contact with Fixtures
4.10.1 Hot Equipment
Flexible air ducts shall be installed with a minimum clearance to an appliance as specified in the appliance manufacturer ’ s installation instructions. They shall not be installed in contact with boilers, steam pipes, or other equipment that exceeds the duct manufacturer ’ s maximum recommended use temperature.
4.10.2 Pipes
Contact with pipes, both metal and plastic, should be avoided when possible, but incidental contact with pipes should not cause damage to the flexible duct. Pipe manufactures instructions must be used to determine if contact with the flexible ducting will lead to degradation in the piping material.
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