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INSPECTION & INSTALLATION INSPECTION & INSTALLATION
4.11 Leakage
Flexible duct has inherently low leakage properties due to the impervious nature of the materials used as the air barrier. These give the flexible duct itself leakage rates less than 0.5% of air volume when proper connections are made to the other systems.
A higher than expected leakage rate can occur at connections if improper materials or careless work practices are used. To assure a low leakage rate for flexible duct systems, the following is required:
• Reference applicable industry manuals (SMACNA, NAIMA) for making round tap - ins into and sealing fitting joints to rigid ducts, plenums, etc. • Make flexible duct connections/splices in accordance with the manufacture ’ s recommended installation instructions for this Standard. • Seal flexible duct connections with sealing materials listed and labeled to Standard UL 181B. Mechanically secure connections with approved clamping material. • Repair any rip, tear or hole in the air barrier using materials listed and labeled to Standard UL 181B and methods recommended by the manufacturer.
4.12 Condensation
In areas with high humidity, it is possible for condensation to form on flexible duct surfaces. Condensation will form when the temperature of any surface is lower than the dew point temperature of the surrounding air. This phenomenon is commonly observed on a glass of ice water placed in a warm, humid environment. It is important to note that ducts with high R - value insulation can decrease the likelihood of condensation. For correct thermal performance, the duct needs to be exposed to ambient air on all sides without insulation compression.
To reduce condensation there are several installation practices to avoid when working in areas prone to condensation.
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4.12.1 Practices to Avoid
4.12.1.1 Duct Contact
When ducts make contact, the temperature between the ducts could easily drop below the dew point temperature. (Figure 21)
Figure 21
4.12.1.2 Insulation Compression
Compressing the thickness of duct insulation significantly impacts duct thermal performance resulting in surface condensation. Avoid compressing the duct insulation.
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