Ductwork for air-handling systems
Construction and sealing of ducting for HVAC and exhaust systems.
Overview
AS 4254 covers duct construction (rigid in Part 2, flexible in Part 1) and sealing for air-handling systems. With increased focus on energy efficiency and sealing in NCC 2022, duct sealing class matters more than it used to.
Key Requirements
- Duct material and gauge.
- Sealing class (A, B, C) — Class C is the most airtight.
- Support and hanging requirements.
- Insulation where ducts pass through unconditioned space.
How it's used in the NCC
Referenced for HVAC services under Part 13.5 of the Housing Provisions.
Practical Notes
- Leaky ducts in roof spaces wreck the energy efficiency rating — common cause of failed verification.
- Insulate any duct in an unconditioned roof space, even short runs.
Where to obtain
The full text of AS 4254 is published by Standards Australia and must be purchased — typical price A$150–400 per part. Always work from the current edition referenced in the NCC, not an older one.