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INSPECTION & INSTALLATION INSPECTION & INSTALLATION
4.12.1.3 Insulation Contact
Avoid laying duct directly on attic insulation in areas conducive to condensation.. Ducts should be properly suspended to allow free circulation of ambient air around all surfaces of the duct. See section 4.5 for proper duct support.
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4.12.1.4 Adding External Insulation
Avoid adding extra insulation to the outside of the duct. 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. 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.
4.12.1.5 Tight Strapping
Avoid installing duct supports too tightly this can lead to surface condensation.
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4.12.1.6 Exposed Metal Fittings
Exposed metal fittings lead to condensation. All metal fittings should be insulated per the requirements in the building code.
4.12.1.7 Improper Sealed Inner Core
Avoid air leakage from flexible duct inner cores. Unconditioned air permeating the surround insulation leads to surface condensation.
4.12.1.8 Porous Inner Core
The use of porous inner liners should be avoided in areas conducive to condensation. (i.e. Perforated Acoustical Products)
4.12.1.9 Torn or Unsealed Vapor Barriers
Air infiltration through the exterior vapor barrier can result in condensation formation on the exterior of the inner liner.
4.13 Field Alterations
Alterations made in the field, such as applying additional overwraps of insulation or barriers, adding spray - foam insulation, surface painting, applying internal sanitizers or spray sealants, etc. may compromise the fire safety performance of the duct and void the manufacturer ’ s listing and/or product warranty.
4.14 Personal Protective Equipment
Insulated flexible air ducts generally contain fiberglass insulation and steel wire. Where necessary, wear eye protection, use a properly fitted approved respirator, and wear long - sleeve loose fitting clothing and gloves during installation.
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