Flexible Installation. Predictable Performance.
Semi-rigid aluminium ducting Spiro-Set is a lightweight HVAC duct system formed in a continuous spiral with a four-ply lock seam. This creates an airtight duct that can be easily cut and hand-bent on site.
Designed to hold its shape after installation, Spiro-Set supports consistent airflow and is self-supporting in standard 3-metre lengths. Used by HVAC contractors, mechanical engineers, and specifiers across New Zealand and Australia, it bridges the gap between flexible and rigid ducting.
Why Choose Spiro-Set Semi-Rigid Ducting?
- Holds its shape for consistent airflow
- Hand-bendable on site, reducing the need for additional fittings
- Airtight four-ply lock seam construction
- Self-supporting in standard 3-metre lengths
- Available in plain, thermally insulated, and acoustic insulated options
Ideal Applications
- Commercial HVAC systems
- Exposed ceiling installations
- Retrofit projects and restricted ceiling spaces
- VAV, variable air volume, connections
- Noise-sensitive areas using the acoustic insulated option
Semi-Rigid vs Flexible vs Rigid Ducting
| Criteria |
Spiro-Set |
Spiro-Flex |
Spiro-Loc |
| Type |
Semi-rigid aluminium ducting |
Flexible ducting |
Rigid steel ducting |
| Airflow consistency |
High |
Lower |
Highest |
| Installation |
Hand-bendable on site |
Compressible and flexible |
Requires fittings and fabrication |
| Self-supporting span |
Yes |
No |
Yes |
| Best suited for |
Commercial HVAC, retrofits, exposed ceilings, and VAV connections |
Short flexible duct runs |
Main duct runs and long spans |
Spiro-Set: Semi-Rigid Ducting Features
Consistent Airflow Performance
Spiro-Set retains the required configuration after installation, helping preserve system design intent and reduce airflow variability over the life of the building. Unlike flexible ducting, it will not collapse or compress under normal thermal cycling or vibration.
Faster, Simpler Installation
Spiro-Set can be hand-bent on site without the need for additional fittings, helping reduce installation time and labour costs compared with rigid spiral ducting. This makes it well suited to retrofit projects and tight ceiling cavities where rigid ducting may be impractical.
Installation should be carried out in accordance with AS 4254.1-2012.
Airtight Construction
The four-ply lock seam creates an airtight duct, supporting overall HVAC system efficiency and helping reduce leakage.
Black Finish Options for Exposed Installations
Spiro-Set is supplied with a black inner finish as standard. For exposed ceiling and architectural applications where the duct is visible, a black outer finish is available on request — allowing Spiro-Set to meet both performance and aesthetic requirements without additional painting or cladding.
- Black inner finish: standard on all Spiro-Set ducting
- Black outer finish: available for exposed ducting applications
- Suited to hospitality, retail, and commercial fit-outs where ductwork is left visible
Available Semi-Rigid Ducting Options
- Type SPU – Plain, uninsulated: aluminium liner only. Available in sizes 75 to 500 mm.
- Type SPI-FP – Plain, insulated: aluminium liner with lofted polyester blanket and 100-micron polyethylene vapour barrier outer sleeve. Available in sizes 100 to 500 mm. Thermal resistance R1.0 m²K/W.
- Type SAI-FP – Acoustic, insulated: perforated aluminium liner with lofted polyester blanket and 100-micron polyethylene vapour barrier outer sleeve. Available in sizes 100 to 300 mm. Thermal resistance R1.0 m²K/W.
Spiro-Set Technical Specifications
| Liner material |
Aluminium, spiral-formed, four-ply lock seam |
| Insulation |
Lofted polyester blanket, R1.0 m²K/W, tested to AS/NZS 4859.1 |
| Outer sleeve |
100-micron flame-retarded polyethylene vapour barrier, low density, high impact |
| Standard diameters |
75, 100, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, and 500 mm |
| Standard length |
3 m, with other lengths available to special order |
| Maximum velocity |
20 m/s |
| Maximum working pressure |
±1.5 kPa, plain liner |
| Temperature range |
-7°C to +70°C, polyethylene jacket |
Acoustic Performance: Type SAI-FP
Acoustic Spiro-Set uses perforations in the inner aluminium core to increase attenuation. The table below shows estimated in-duct insertion loss for a 3-metre length, tested in accordance with the Air Diffusion Council Flexible Air Duct Test Code FD 72-R1.
| Diameter |
Octave Band Centre Frequency, Hz: Insertion Loss, dB |
|
63 |
125 |
250 |
500 |
1000 |
2000 |
4000 |
8000 |
| 150 mm |
13.2 |
18.9 |
24.5 |
29.5 |
25.9 |
29.2 |
14.4 |
9.3 |
| 200 mm |
15.8 |
23.0 |
20.5 |
29.0 |
28.7 |
25.8 |
10.9 |
7.6 |
| 300 mm |
18.1 |
26.5 |
21.3 |
25.6 |
19.4 |
14.4 |
7.0 |
4.9 |
Note: Values are based on ideal laboratory conditions, with ducting fully extended and straight. Site bends and connections may increase overall attenuation.
Testing and Compliance
- Complies with AS 4254, AS 1530.3, and UL 181 where applicable
- Meets NZBC C/AS1 Part 6 requirements for control of internal fire and smoke spread
- EFH indices: ignitability 0, spread of flame 0, heat evolved 0, smoke developed 1
- BRANZ Test Certificate FE1681 to AS 1530.3
- BRANZ Opinion No. 92/264
- Insulation tested to AS/NZS 4859.1, thermal resistance R1.0 m²K/W
