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INSPECTION & INSTALLATION
4.6 Compression
Unnecessary longitudinal and circumferential compression of flexible duct significantly increases pressure drop resulting in reduced air flow and loss of system efficiency. Care should be taken to insure flexible ducts are installed fully extended and not compressed. A simplified, yet easily understood, comparison can be made by looking at the common garden water hose. Kinking a garden hose reduces or chokes off the water flow. Also, a long garden hose will have lower water pressure than a much shorter one. Movement of air through ducts is effected in the same manner.
4.6.1 Longitudinal Compression.
Flexible air ducts and air connectors should always be installed to their fullest length without longitudinal compression. Due to the helical configuration of flex duct inner cores, excess longitudinal compression significantly increases pressure drop and reduces performance. (See Figure 19)
4.6.2 Circumferential Compression.
Flexible air ducts and air connectors are intended to be installed in their original round configuration. For optimal air flow, care should be taken to avoid compressing the duct circumferentially along its length. Ducts should not be forced into small building cavity areas that result in compression of the duct wall and/ or the duct inner liner diameter. Incidental compression when connecting to oval pipe or fittings is acceptable. Compressing the duct vapor barrier and insulation can reduce the duct thermal performance characteristics and could also result in localized condensation. (See Figure 20)
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Figure 19
Figure 20
4.7 Installation Instructions
All connections, joints and splices shall be made in accordance with the manufacturer ’ s installation instructions. Always reference the manufacturer ’ s installation instructions for more detailed requirements.
Due to the wide variety of ducts and duct assemblies with special end treatments (factory installed fittings, taped ends, crimped metal ends, etc.), only the standardized installation instructions were shown.
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