Legislation Updates

Update to flexible duct standard

The draft standard AS 4254.1 Ductwork for air-handling systems in buildings, Part 1: Flexible duct is open for comment until November 18.

The document provides standardised requirements for the performance testing, manufacture and installation of flexible ducts in order to improve their thermal performance. It is particularly relevant for specifiers, manufacturers, regulatory authorities and installers of air-handling systems for buildings.

Independent market audits and studies in Australia and the USA have estimated thermal energy losses in the vicinity of 20 per cent to 40 per cent in flexible duct systems due to poor installation practices and insulation being thermally deficient for the application into which it is installed.

The National Construction Code requires different thermal ratings for insulation used on flexible duct, depending on the climate zone and the application it is installed into. This, in conjunction with the increased energy efficiency requirements for new constructions, and rising costs of energy, is driving the requirement for more efficient flexible duct systems.

One major change in this revised version is the proposed addition of a formal test method for testing and certifying the R-values for flexible duct.

Currently, flexible duct manufacturers buy insulation with a stated R-value from an insulation manufacturer to produce a piece of flexible duct with a stated R-value. The proposed test method formalises a test procedure so that a piece of manufactured duct gets sent to a certified testing authority for its R-value to be assessed.

Another important change in the standard is the clarification and expansion of allowable methods to hang flexible duct. Ambiguity around the interpretation of the wording in the standard has now been clarified.

The changes are aimed at preventing kinks that restrict airflow, and hanging straps that dig into or compress the insulation wall of the duct and cause cold bridging and condensation.

Other changes include the modification of requirements for applying duct tape to provide total air and vapour seal, and the provision for sag in hanging of 120mm between supports.

You can provide feedback on the draft standard through Standard Australia’s public commenting portal.

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