What is AS 1668.2 and when was it last updated?

AS 1668.2 is the Australian Standard titled 'The use of ventilation and airconditioning in buildings - Part 2: Mechanical ventilation in buildings'. The current edition is AS 1668.2:2024, which superseded AS 1668.2:2012. It is the primary reference for mechanical ventilation design in Australian buildings and is called up by the National Construction Code (NCC) Volume One Section F4 (Health and Amenity) and Volume Two for Class 1 buildings. AS 1668.2 specifies outdoor air rates, contaminant removal rates and exhaust requirements for kitchens, bathrooms, car parks, lab fume cupboards, and other regulated spaces.

What is the difference between AS 1668.1 and AS 1668.2?

AS 1668.1:2015 covers fire and smoke control in buildings — it specifies smoke management systems, stair pressurisation, smoke spill systems and smoke exhaust. AS 1668.2:2024 covers general mechanical ventilation — outdoor air for occupants, exhaust for contaminant removal, and pressurisation control. Most Australian buildings need to comply with both standards: AS 1668.1 for life safety in fire scenarios, AS 1668.2 for everyday indoor air quality. The two standards reference each other and share the same series numbering for clarity. AS 1668.4:2012 is the third part, covering natural ventilation, but is less commonly cited.

How does AS 1668.2 relate to ASHRAE 62.1?

AS 1668.2 and ASHRAE 62.1 cover the same domain (outdoor air ventilation for indoor air quality) but use different methodologies. ASHRAE 62.1 uses a sum-of-people-plus-area calculation (Rp + Ra approach), while AS 1668.2 historically used a single per-person rate that has gradually moved closer to the ASHRAE approach in the 2024 revision. For most office and retail space, ASHRAE 62.1 and AS 1668.2 yield similar outdoor air rates within ±10%. For specialty space (laboratories, kitchens, hospitals), the standards diverge more significantly and the Australian designer must follow AS 1668.2. SBKJ engineers familiar with both standards routinely cross-check designs to verify the more conservative outcome is met.

What duct construction does AS 1668.2 require?

AS 1668.2 itself does not specify duct construction in detail — it references AS 4254 (Ductwork for air-handling systems in buildings) for that. AS 4254.1 covers flexible duct, AS 4254.2 covers rigid duct construction. Typical commercial Australian projects specify Pittsburgh-lock galvanized rectangular duct or spiral round duct from AS 4254-listed materials, sealed to AS 4254 Class B (medium pressure). High-performance projects (data centres, hospitals, cleanrooms) move to Class A. Stainless construction is required where AS 1668.2 calls out chemical fume exhaust (Section 5) or where the project specification overrides for sanitary applications.

What are the AS 1668.2 outdoor air rates for offices?

Under AS 1668.2:2024 Table A1, an office space requires 7.5 L/s per person of outdoor air, plus 0.5 L/s per square metre of floor area for building-related contaminants. For a typical 100 m² office with 10 occupants, that yields 7.5 × 10 + 0.5 × 100 = 125 L/s = 7,500 L/min = 450 m³/h of outdoor air. The supply air flow rate is normally higher to account for cooling/heating load — 5 L/s/m² is a typical commercial office supply rate, so for 100 m² that's 500 L/s of total supply with 125 L/s outdoor air, giving 25% outdoor air fraction. SBKJ rectangular duct sizing for 500 L/s at 5 m/s velocity is approximately 250 mm × 400 mm.

How does AS 1668.2 handle kitchen exhaust?

AS 1668.2 Section 6 covers commercial kitchen exhaust. Type 1 (grease and smoke) hoods require minimum exhaust rate based on appliance type — typically 0.18 to 0.50 m³/s per linear metre of hood depending on cooking equipment. Type 2 hoods (heat and moisture only) require 0.10 to 0.30 m³/s per linear metre. Hood capture velocity must be at least 0.25 m/s at the hood face. The exhaust duct must be 304 stainless minimum (or 316 in coastal/chloride atmospheres), continuously welded longitudinal seam (NOT Pittsburgh-lock), sloped to a grease reservoir, with cleanout access at every change of direction. NFPA 96 requirements often supplement AS 1668.2 for franchise kitchens (McDonald's, KFC, Hungry Jack's) operating to global brand standards.

What about lab fume cupboard exhaust under AS 1668.2?

AS 1668.2 Section 7 covers fume cupboard exhaust, cross-referenced with AS/NZS 2243.8 (Safety in laboratories). Standard fume cupboards require 0.5 m/s minimum face velocity with the sash open (typical), or 0.3 m/s for low-flow VAV cabinets with sash management. Duct construction must be 316L stainless steel (chloride and acid resistance) with all-welded seams; PVC or FRP is acceptable for purely acidic streams (HCl, H2SO4) but requires fire risk assessment. Perchloric acid hoods need a separate washdown duct system to prevent perchlorate salt accumulation. Radioisotope hoods often need HEPA on exhaust. SBKJ stainless spiral tubeformers are the standard fabrication route for lab exhaust trunks.

How does AS 1668.2 interact with NCC Section J?

NCC Volume One Section J (Energy Efficiency) sets minimum performance for HVAC system energy use, while AS 1668.2 sets minimum outdoor air for indoor air quality. The two standards interact at the design point: AS 1668.2 sets a floor on outdoor air, NCC Section J pushes you toward demand-controlled ventilation (DCV) and heat recovery to minimise the energy penalty of that outdoor air. NCC J5 mandates heat recovery on systems exceeding a threshold (typically >1000 L/s outdoor air), and DCV with CO2 sensors is the most common compliance path for variable-occupancy space (offices, classrooms, retail). The duct system must support DCV — variable-volume terminals, sensible airflow modulation, low-leakage construction (SMACNA Class A or AS 4254 Class A) so the energy savings are not eroded by leakage.

Standards Reference

AS 1668.2 Australian Mechanical Ventilation Code — Reference Guide for HVAC Duct Specification

AS 1668.2:2024 is the working document every Australian HVAC designer reads three times a week and every fabricator gets handed at the start of a project but rarely reads cover-to-cover. This reference distils the parts that matter for HVAC duct fabrication — outdoor air rates, exhaust requirements, smoke management interaction, kitchen and laboratory provisions, and the duct construction implications — into the format SBKJ engineering uses internally to scope projects in the Australian market.

Maintained by SBKJ Engineering Team · Published May 9, 2026 · Reviewed by SBKJ Senior Engineers

What AS 1668.2 covers and what it doesn't

AS 1668.2:2024 is titled The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings. Published by Standards Australia, it superseded AS 1668.2:2012 and is the primary technical reference cited by the National Construction Code (NCC) Volume One Section F4 (Health and Amenity) for mechanical ventilation requirements in Class 2 to 9 buildings, and Volume Two for Class 1 buildings (residential houses). Where the NCC says “mechanical ventilation system shall comply with AS 1668.2” — which it does in roughly 30 places — that's the reference being invoked.

The standard does not cover:

Fire and smoke control — that's AS 1668.1:2015
Natural ventilation — that's AS 1668.4:2012 (or the deemed-to-satisfy provisions of NCC Volume One Section F4.5)
Ductwork construction details — that's AS 4254.1 (flexible duct) and AS 4254.2 (rigid duct)
Refrigeration safety — that's AS/NZS 1677 series
Equipment selection — manufacturers' specifications and AHRI/Eurovent ratings
Energy efficiency — NCC Section J handles that

So AS 1668.2 is the ventilation rate and contaminant removal reference. It tells you how much outdoor air every space needs, how much exhaust every kitchen and lab and bathroom needs, and how the building must be pressurised to control contaminant migration. The duct construction that delivers those rates is governed by AS 4254 and the project specification.

The 2024 revision — what changed

AS 1668.2:2024 was published in March 2024 and is substantively different from the 2012 edition that preceded it. Key changes for HVAC duct designers:

Outdoor air calculation method — moved closer to ASHRAE 62.1's split between people-related (V_p) and area-related (V_a) components. Previous editions used a single per-person rate with floor-area adjustment factor; 2024 uses an explicit additive method.
Higher outdoor air rates for high-density occupancies — classrooms, gyms, courtrooms, religious assembly all increased by 10-25% to reflect contemporary IAQ research.
Reduced rates for lower-density spaces — private offices, conference rooms with sustained low occupancy can now be designed with lower nominal rates and demand-controlled ventilation (DCV) provisions.
Recognition of MERV 13+ filtration credits — high-efficiency filtration can offset some outdoor air requirement in retail and office space (similar to ASHRAE 62.1 IAQ procedure).
Expanded car park provisions — CO sensor-based ventilation now mandated for car parks >1000 m² under car-park section, replacing earlier prescriptive air change rate.
Tightened lab fume cupboard requirements — minimum face velocity 0.5 m/s sash-open (previously 0.4 m/s), with VAV/DCV sash management explicitly recognised.
New recognition of UV-C and bipolar ionisation — with caveats about secondary by-product formation; not endorsed but no longer prohibited.
Clearer interaction with NCC Section J — aligned cross-references with the 2022 NCC update.

Outdoor air rates by space type (Table A1 summary)

The heart of AS 1668.2 is Table A1, which lists outdoor air requirements per space type. The table is too detailed to reproduce in full here (and copyright restrictions prevent full reproduction in any case), but the format is consistent across categories:

V_p (person rate) in L/s per person — covers occupant-generated contaminants (CO2, body odour)
V_a (area rate) in L/s per square metre — covers building-fabric and finishes off-gassing
Total = (V_p × persons) + (V_a × floor area)

Indicative rates (always check the current standard for the exact value):

Office (general) — V_p 7.5 L/s/person, V_a 0.5 L/s/m²
Conference/meeting room — V_p 7.5 L/s/person, V_a 0.3 L/s/m²
Classroom (primary/secondary) — V_p 8.0 L/s/person, V_a 0.5 L/s/m²
Lecture theatre — V_p 8.0 L/s/person, V_a 0.3 L/s/m²
Retail (general) — V_p 4.0 L/s/person, V_a 0.6 L/s/m²
Restaurant/dining — V_p 5.0 L/s/person, V_a 1.0 L/s/m²
Bar/lounge — V_p 5.0 L/s/person, V_a 2.0 L/s/m²
Hospital ward (general) — V_p 12.5 L/s/person, V_a 1.0 L/s/m²
Hospital operating theatre — refer to AS/NZS 2243.3 and ASHRAE 170; AS 1668.2 defers
Hotel guest room — V_p 5.0 L/s/person, V_a 0.3 L/s/m² (typical 2-person room with 25 m² gives 17.5 L/s)
Sports hall — V_p 10.0 L/s/person, V_a 0.3 L/s/m²
Indoor swimming pool hall — V_a 6 L/s/m² of pool surface (not per person)
Place of worship — V_p 5.0 L/s/person, V_a 0.3 L/s/m²
Library reading room — V_p 7.5 L/s/person, V_a 0.3 L/s/m²
Museum gallery — V_p 5.0 L/s/person, V_a 0.3 L/s/m² (with separate temperature/RH precision; refer ASHRAE handbook)

Exhaust requirements (Section 5)

Section 5 of AS 1668.2 covers contaminant exhaust. The most-quoted provisions:

Bathrooms (Class 2-9 buildings) — minimum 25 L/s per WC fixture, or 10 air changes per hour, whichever is greater. Ducted directly to outside; cannot discharge into ceiling space or another room.
Showers — minimum 25 L/s per shower, or 10 ACH; intermittent operation acceptable with humidistat or motion sensor control.
Public toilets — 10 L/s per cubicle continuous, or 25 L/s per cubicle if intermittent.
Photocopier/print rooms — 10 L/s per machine, dedicated exhaust to outside.
Battery rooms — calculated based on hydrogen evolution rate; typically 4-6 ACH for sealed lead-acid, higher for flooded.
Cool rooms (walk-in) — refrigerant safety exhaust per AS/NZS 1677.
Smoking rooms — 25 L/s per occupant, separate exhaust, negative pressure to adjacent space (largely deprecated by national workplace smoking bans, but provisions remain in standard).
Loading docks (enclosed) — CO and NOx-based ventilation, typically 5-10 ACH continuous.

Kitchen exhaust (Section 6)

Section 6 covers commercial kitchen ventilation. Key requirements:

Type 1 hoods (grease and smoke) — over deep fryers, char grills, woks, salamanders, conveyor pizza ovens, gas ranges. Exhaust rate 0.18 to 0.50 m³/s per linear metre of hood depending on appliance heat output.
Type 2 hoods (heat and moisture only) — over dishwashers, steamers, ovens with no grease laden vapour. Exhaust rate 0.10 to 0.30 m³/s per linear metre.
Capture velocity — minimum 0.25 m/s at hood face (typical 0.4-0.5 m/s in design).
Make-up air — 80-90% of exhaust volume; can be dedicated MUA unit or transfer from adjacent dining (with provisions).
Duct construction — 304 stainless steel minimum (316 in coastal/chloride atmospheres), continuously welded longitudinal seam, sloped to a grease reservoir at every vertical riser bottom, cleanout access doors at every change of direction or every 3.7 m horizontal run.
Fire suppression — Ansul R-102 or equivalent listed wet chemical system per AS/NZS 1841 series.
Velocity — minimum 7.6 m/s in horizontal runs to maintain grease entrainment; 4 m/s minimum in vertical risers.

These requirements largely align with NFPA 96 (the US standard most international franchise kitchens default to). McDonald's, KFC, Hungry Jack's, Domino's and most Australian QSR chains specify NFPA 96 in their global brand standard, which exceeds AS 1668.2 in some respects (continuous welded vs spot-welded, larger access doors). SBKJ stainless ductwork machinery supports both standards from the same machine configuration.

Laboratory fume cupboard exhaust (Section 7)

Section 7 covers laboratory exhaust, with cross-references to AS/NZS 2243.8 (Safety in laboratories — Fume cupboards) and AS/NZS 2243.3 (Microbiological safety and containment).

Fume cupboard face velocity — minimum 0.5 m/s sash-open (2024 revision; was 0.4 m/s in 2012 edition). VAV cupboards with active sash management can reduce to 0.3 m/s with monitoring.
Fume cupboard sash position — designed for the working sash position (typically 500 mm open); face velocity must be maintained at all sash positions for VAV designs.
Duct material — 316L stainless steel for general lab exhaust; PVC, PP or FRP for purely acidic streams (HCl, H2SO4, HNO3) with fire risk assessment; 316L mandatory for HF (hydrofluoric acid) and perchloric acid hoods.
Perchloric acid hoods — require dedicated washdown system and cannot share duct with any other hood; perchlorate salt accumulation is an explosion hazard.
Radioisotope hoods — HEPA H13 or H14 on exhaust before atmospheric discharge.
Cytotoxic drug cabinets (Class II Biological Safety Cabinet) — covered by AS/NZS 2252 series; total exhaust through HEPA discharged to outside or partial recirculation through HEPA depending on cabinet class.
Discharge velocity — minimum 12 m/s upward, minimum 3 m above roof, away from any air intake by 30 m horizontal or 8 m vertical.

Pressurisation control (Section 4)

AS 1668.2 Section 4 covers building pressurisation. The most-cited provisions:

Positive pressurisation — building should be slightly positive (5-15 Pa) relative to outside to prevent dust and pollen ingress through envelope leakage.
Stair pressurisation — covered by AS 1668.1, not 1668.2; called out for cross-reference.
Internal pressure cascades — maintained by exhaust quantity, not supply quantity; corridors negative to clean rooms (cleanrooms supply more than exhaust), corridors positive to dirty zones (dirty zones exhaust more than supply).
Hospital cascades — defer to AS/NZS 2243.3 and ASHRAE 170; AS 1668.2 acknowledges but does not replicate.
Industrial cleanroom cascades — defer to ISO 14644-4; AS 1668.2 acknowledges.

Car park ventilation (Section 8)

Section 8 covers enclosed car park ventilation. The 2024 revision:

CO concentration limits — 30 ppm 8-hour TWA, 60 ppm 30-minute peak.
NO_x control — new in 2024 reflecting diesel car emissions; design to limit NO₂ to 1 ppm 8-hour.
Sensor-based ventilation — mandatory for car parks >1000 m²; CO sensors and NO₂ sensors zoned per 1000 m² or per level.
Jet fan systems — recognised as alternative to ducted ventilation in clear-bay car parks; design to AS/NZS standards or international best practice.
EV charging zones — new section in 2024 reflecting battery thermal events; consider thermal runaway smoke and gas exhaust separately from CO ventilation.

Smoke management interaction with AS 1668.1

Although AS 1668.1 (smoke management) is the relevant standard for fire scenarios, the day-to-day mechanical ventilation system designed under AS 1668.2 must be compatible. Three interaction points:

Smoke spill duct sizing — if the 1668.2 design includes risers used for smoke spill in fire mode (1668.1), the duct must be sized for the larger of the two flows, with fire dampers and/or duct insulation to maintain integrity at elevated temperature.
Pressurisation system fans — stair pressurisation fans (1668.1) often share AHU plant rooms with general supply fans (1668.2); ensure the smoke mode operation does not fail due to supply fan operating at a conflicting setpoint.
Duct construction — 1668.1 smoke spill duct must be FRL-rated (Fire Resistance Level) to AS 1530.4 if it passes through fire compartments. SBKJ duct can be specified with FRL fire-rated wrap or insulation for these dual-purpose runs.

Ductwork construction implications (AS 4254 cross-reference)

AS 1668.2 sets the airflow rate. AS 4254 governs how the duct that carries that airflow is built. Key implications for the SBKJ machine specification:

AS 4254 Class B (medium pressure) — commercial offices, retail, hotels. Pittsburgh-lock galvanized rectangular duct; SBAL-II or SBAL-III auto duct line is typical. SMACNA Seal Class B equivalent.
AS 4254 Class A (high pressure) — data centres, hospitals, cleanrooms. TDF flange rectangular duct or welded-seam spiral; SBAL-V is typical with stainless option. SMACNA Seal Class A equivalent.
Stainless construction — required for kitchen exhaust (Section 6), lab fume exhaust (Section 7), some healthcare applications (HVAC for pharmacy clean rooms). 304 minimum, 316 for chloride exposure. SBAL-V stainless or SBTF spiral stainless.
FRL fire rating — smoke spill duct under 1668.1, kitchen exhaust passing through fire compartments. Achieved with field-applied wrap (Promat, Kingspan KoolDuct fire-rated) or factory-coated stainless duct.

NCC Section J interaction

NCC Volume One Section J (Energy Efficiency) sits alongside AS 1668.2 and pushes designers toward energy-efficient delivery of the 1668.2 minimum airflow:

NCC J5.4 — Heat recovery. Mandatory on systems exceeding the threshold (typically >1000 L/s outdoor air for cooling, >500 L/s for heating). Sensible heat exchanger or enthalpy wheel acceptable.
NCC J5.7 — Demand-controlled ventilation (DCV). Required for variable-occupancy space: classrooms, retail, conference rooms. CO2 sensor-based modulation of outdoor air, with floor of 30% of design rate.
NCC J6 — Fan power limit. Total fan power limited to a function of supply air flow (typical limit 1.4 W/L/s for VAV, 2.0 W/L/s for CAV). Ductwork pressure loss must be designed accordingly — high-leakage duct erodes fan power compliance.
NCC J7 — Duct sealing and insulation. AS 4254 Class A or B mandatory; NCC J7 specifies the leakage class threshold.

Common AS 1668.2 design mistakes

Designing to V_p only and ignoring V_a. Older designers used the per-person rate alone; the 2024 revision explicitly requires both components. For a low-density space (open-plan office at 10 m²/person), V_a can dominate the calculation.
Forgetting the kitchen exhaust make-up air. A 5,000 L/s kitchen hood needs roughly 4,500 L/s of make-up air; transfer from dining is acceptable up to a point, but a dedicated MUA unit is usually required and that air still has to be conditioned.
Ducting bathroom exhaust into the ceiling space. AS 1668.2 explicitly requires direct discharge to outside — ceiling space discharge is a fail in the post-occupancy compliance audit.
Specifying galvanized for kitchen or fume cupboard exhaust. Section 6 and Section 7 both effectively require stainless. Galvanized fails the corrosion test within 2 years and triggers a re-fabrication contract.
Missing the 2024 face-velocity bump. Fume cupboard face velocity went from 0.4 m/s to 0.5 m/s. Designs sized for 0.4 m/s under the 2012 edition need recalculation if the project is being permitted under the 2024 standard.
Ignoring NCC J5.4 heat recovery. A 2,000 L/s outdoor air system without heat recovery exceeds J5.4 threshold and fails Section J. Heat recovery wheel or plate exchanger needs to be designed in from the start, with duct routing accommodating the heat recovery position.
Not co-ordinating with AS 1668.1 smoke spill. If the project has a fire engineering report calling for smoke spill via the supply duct, the supply duct sizing and FRL must accommodate that. Late discovery of this in design is the most common cause of project re-design.

How SBKJ machinery supports AS 1668.2-compliant duct fabrication

SBKJ's machine platform is designed to support every duct construction class AS 1668.2 implicates:

SBAL-III auto duct line — galvanized Pittsburgh-lock rectangular for AS 4254 Class B commercial and residential work. The bread-and-butter of Australian commercial mechanical contractors.
SBAL-V auto duct line — TDF flange rectangular for AS 4254 Class A high-pressure work; stainless configuration for Section 6 kitchen exhaust and Section 7 lab exhaust.
SBTF-1602 spiral tubeformer — round spiral duct, galvanized or stainless, with optional welded longitudinal seam for high-spec work.
TIG seam welder — stand-alone unit for shops that need welded duct capability without a full SBAL-V upgrade. Typically paired with kitchen exhaust contractors.
F350 continuous seam welder — for high-volume stainless fabrication where Section 6 kitchen exhaust or Section 7 lab exhaust dominates the work mix.

Talk to SBKJ engineering

SBKJ engineering supports Australian fabricators on AS 1668.2 / AS 4254 / NCC Section J compliance. We can help you:

Validate your duct fabrication setup against the AS 4254 leakage class your project specifies
Scope a stainless-capable SBAL-V or F350 for kitchen and lab exhaust work
Provide AS-compliant material certificates and weld procedure qualifications (WPQR) for 304/316 stainless
Cross-reference NCC Section J fan power and heat recovery requirements with your machine selection

Contact SBKJ engineering