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CHAPTER 4: INSPECTION & INSTALLATION
4.1 Installation Key Points
SIZED - Flexible duct shall be properly sized per the requirements of ACCA Manual D or Manual Q as applicable .
Time should be taken to complete sizing calculations for air distribution systems. This is not specific to flexible duct systems, any ducting system should be properly sized per the requirements of ACCA Manual D (Residential) or Manual Q (Commercial).
ROUTED - Flexible duct runs shall be properly routed to minimize sagging and “ snaking ”
Ducting systems should ALWAYS run in the most direct path from starting point to termination point. Every unnecessary turn or sag in the duct increases friction and reduces air flow.
EXTENDED - Flexible duct shall be installed fully extended using the minimum length needed to make connections.
Along with being installed in the most direct path the ducting should be fully extended. Ducting that is not extended can increase pressure drop and reduce air flow.
BENDED - Flexible duct bends shall be greater than or equal to 1 duct diameter.
Sharp bends in ducting significantly increase pressure drop. Keep bends to great than or equal to one (1) duct diameter and properly supported.
SUPPORTED - Flexible ducts shall be properly supported.
Duct supports shall be a minimum of 1.5” in width with wider supports recommended in installation areas conducive to condensation. Horizontal duct runs shall be supported at maximum 4’ intervals and vertical risers at maximum 6’ intervals.
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SEPARATED - Flexible ducts should be separated in areas conducive to condensation.
To prevent condensation forming on the outer surface of the duct, a gap should be present to allow free air flow over the outer duct surface. Locations where two duct surfaces are in contact can lead to condensation.
SEALED - Flexible duct connections shall be properly sealed using listed and labeled sealing materials and methods.
Care shall be taken to properly seal the ducting using materials listed and labeled to the UL standard. Improper sealing and installation methods can lead to leakage which can reduce system efficiency.
Note: An Installation Checklist can be found in Appendix E of this manual. This checklist can be used by installers or inspectors to ensure that the ducting is installed properly.
4.2 Air Duct or Air Connector
Flexible ducts are classified by their performance when tested to UL 181 Standard for Safety, Factory - Made Air Ducts and Air Connectors. The standard includes seventeen (17) tests covering fire testing, tests for physical characteristics, and product performance testing. Sixteen (16) test are applicable to Air Ducts and thirteen (13) tests are applicable to Air Connectors. One (1) is reserved for testing Joining Materials. (Refer to Appendix B for testing detail.)
In many cases, Air Ducts and Air Connectors look similar in appearance. The only way to be sure whether a flexible duct is an Air Duct or Air Connector is to examine the listing label on the product.
• Flexible Air Ducts will have a rectangular or square listing label and include the words “ Air Duct ”.
• Air Connectors will have a circular listing label which identifies it as an “ Air Connector ”. In addition, Air Connectors will include the words “ For installation in lengths not over 14 ft. ”
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