NFPA 96 Commercial Kitchen Exhaust HVAC Ductwork — Engineering and Fabrication Guide

Why commercial kitchen exhaust ductwork is its own discipline

Commercial kitchen exhaust ductwork is the most heavily regulated category of HVAC duct in any building. The reason is simple: it is the only duct system that, by design, transports a flammable medium — grease vapour — through a building under temperatures that can reach 1,100 degrees Celsius in a fire condition. Every other HVAC duct class is moving conditioned air. A grease duct is moving fuel.

That single fact drives every difference between a kitchen exhaust system and the rest of the HVAC scope. Standard galvanised rectangular duct fabricated on a Pittsburgh-lock seam — the workhorse of office and warehouse ventilation — is explicitly prohibited in Type 1 service by NFPA 96. The reason is not paranoia: galvanising volatilises in a grease fire and Pittsburgh seams blow open under positive pressure. Compliant grease duct is welded, gauged-up, sloped, cleaned-out, suppression-integrated and clearance-controlled because the failure mode is a structure fire, not a comfort complaint.

This guide is the same engineering reference that SBKJ uses with its Australian hotel, hospital and quick-service restaurant customers when they ask what compliant kitchen exhaust ductwork actually looks like — at the spec sheet level, at the fabrication-shop level, and on the roof. We will work through the codes, the materials, the welded construction, the clearance and slope, the suppression interface, and the machinery that fabricates it. By the end you will know exactly what to specify, what to fabricate, and what to refuse to install.

The governing standards: NFPA 96, AS 1668.2, IMC and AS 4674

Australia is a multi-standard jurisdiction for commercial kitchen exhaust. The National Construction Code references AS 1668.2, which has its own kitchen exhaust section, but the corporate engineering standards used by international hotel chains, hospital systems and restaurant brands are almost always written against NFPA 96. In practice, the larger and more risk-averse the operator, the more likely the project will be specified to NFPA 96 with AS 1668.2 as a local overlay.

Here is how the four most relevant standards stack up:

• NFPA 96 (2024 edition) — Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations. The single most prescriptive standard in the world for grease duct. Covers hood classification, exhaust airflow, duct gauge and material, welded seam requirements, clearance to combustibles, slope, velocity, cleanout access, fire suppression, fan listing, roof discharge, grease containment and inspection frequency. Updated triennially. Referenced by virtually every U.S. and international hotel and restaurant brand specification.
• AS 1668.2:2024 Section 6 — Kitchen exhaust. The Australian Standard provision for commercial kitchen exhaust. Covers hood selection, exhaust airflow per appliance class, duct construction (with cross-reference to NFPA 96 for grease duct construction details), make-up air, fan and discharge requirements. Less prescriptive than NFPA 96 on weld details — most Australian fabricators default to NFPA 96 weld specifications because it is the more defensible position when an AHJ inspects.
• IMC Sections 506 and 507 — International Mechanical Code commercial kitchen exhaust. Adopted in most U.S. jurisdictions and many Pacific markets. Section 506 covers commercial kitchen hoods and Section 507 covers commercial kitchen exhaust ducts. IMC 506/507 references NFPA 96 for most prescriptive requirements but adds local enforcement language.
• AS 4674:2004 — Construction and fitout of food premises. Covers the food-safety and hygiene side of kitchen construction including hood capture, surface materials and cleaning access. Less stringent than NFPA 96 on fire and smoke control but mandatory for food premises in Australia.

The practical resolution we see on Australian projects is clear: fabricate to NFPA 96 weld and material specifications, document compliance with AS 1668.2 Section 6 for the local AHJ, and meet AS 4674 for food-premises hygiene. A duct fabricated to NFPA 96 standards automatically meets AS 1668.2 — the converse is not true.

Type 1 versus Type 2 hood classification

The single most consequential decision in commercial kitchen ventilation design is the hood classification. Get this wrong and every downstream specification — duct material, gauge, weld type, clearance, fire suppression — is wrong with it.

The classification is defined by what the appliance produces:

• Type 1 hood — grease-laden vapour. Required over any appliance that generates grease, smoke or flammable particulate. The standard list includes deep fryers, griddles, charbroilers, woks, salamanders, chargrills, conveyor pizza ovens, ranges, and tilt skillets. Type 1 hoods require listed grease filters (UL 1046), welded grease duct construction per NFPA 96, fire suppression coverage, and an upblast grease-rated exhaust fan.
• Type 2 hood — heat, steam and moisture only. Used over appliances that do not produce grease — dishwashers, ovens (when used only for baking), steam kettles, bain-marie water baths, and pasta cookers. Type 2 hoods may use galvanised duct because no grease residue is present and the fire risk is steam, not combustion. Lighter-gauge mechanical-seam construction (Pittsburgh, TDF flange, slip-and-drive) is acceptable.

The grey area sits with combination ovens (combi ovens), conveyor ovens used for some grease-bearing menu items, and tilting skillets used as both bain-marie and skillet. The default-to-Type-1 principle applies: if there is any reasonable likelihood the appliance will at any point in its service life produce grease vapour, the engineer should classify it Type 1. The cost difference between Type 1 and Type 2 ducting is significant — typically 3 to 4 times higher per linear metre — but the cost of a Type 2 duct in Type 1 service is a roof fire and a building loss.

A useful field heuristic: if the chef ever cooks animal protein on it, it is Type 1. If the chef only heats water, vegetables, baked goods or pre-cooked grease-free product, it is Type 2.

Material and gauge specifications

NFPA 96 Section 7.5.1 prescribes the construction materials for grease duct in two paths:

• Field-fabricated carbon steel. Minimum 16 gauge (0.0598 inches / 1.519 mm) cold-rolled carbon steel. Painted exterior is permitted but the interior must be a clean, weldable finish — no zinc coating, no chromate, no oil that interferes with welding.
• Field-fabricated stainless steel. Minimum 18 gauge (0.0478 inches / 1.214 mm) Type 304 or Type 316 stainless. The 18 gauge minimum is acceptable because stainless has higher yield strength and corrosion resistance than carbon steel; the trade-off is roughly 30 percent material cost increase versus carbon steel.
• Listed factory-built grease duct. Constructed under UL 1978 (Standard for Grease Ducts) or FM 4920 (Approval Standard for Pre-Engineered, Factory-Built Grease Ducts). Typically a double-wall design with insulation between the inner duct and outer jacket, allowing zero-clearance installation per the listing. Brands include Van-Packer, DuraVent FasNSeal, Schebler Chimney, Selkirk and AmpcoFlue.

For Australian commercial kitchen work the practical material decision is between 16 gauge carbon steel for back-of-house and concealed runs where corrosion is not a concern, and 18 gauge stainless 304 for any duct exposed to view, in coastal locations, in marine air, or in food-acid-rich environments such as pickling stations and acidic-marinade lines. Stainless 316 is reserved for chloride-rich environments — pool-deck restaurants, beach clubs, marine vessels and coastal hotels with regular salt-spray exposure.

Two material choices that are explicitly prohibited:

• Galvanised steel in Type 1 service. The zinc coating fails through dezincification within 12 to 24 months under sustained grease-vapour exposure, and zinc oxide vapour from a fire is toxic. Galvanised remains acceptable for Type 2 applications.
• Aluminium and aluminised steel in any grease-bearing service. Aluminium melts at 660 degrees Celsius — well below grease fire temperature — and aluminised steel coatings fail by the same mechanism as galvanised.

The welded longitudinal seam — why Pittsburgh-lock fails

The single most important construction detail in NFPA 96 is Section 7.5.2, which requires every grease duct longitudinal seam to be continuously welded with full penetration, external to the duct, and liquid-tight. This is also the most commonly violated requirement in field-fabricated work, because the standard rectangular duct fabrication workflow used in office and warehouse HVAC defaults to a Pittsburgh-lock or snap-lock seam — both of which are mechanical, both of which leak, and neither of which is permitted on grease duct.

Why mechanical seams fail:

• Pittsburgh-lock is a folded mechanical seam with a small bead of mastic for air-tightness. It is gas-tight against low static pressure but not liquid-tight against grease, and it has no tensile strength under fire-condition positive pressure.
• Snap-lock is a slip-fit seam with a folded edge — even less robust than Pittsburgh and never acceptable on grease duct.
• TDF (Transverse Duct Flange) is a flanged transverse joint with corner pieces and gasket — fast and gas-tight but not weld-equivalent and prohibited at transverse grease-duct joints.

The compliant alternatives, in the order most fabricators adopt them:

• TIG seam welding (GTAW). The cleanest finish for stainless 304 and 316 — argon-shielded, autogenous (no filler) for thin gauges, very low heat input, minimal distortion. The gold standard for visible stainless ductwork in open kitchens, hotel banquet kitchens and restaurant pass-through kitchens.
• MIG seam welding (GMAW). Faster than TIG with a slight bead — acceptable for concealed back-of-house carbon steel grease duct where finish is not visible. Most fabrication shops use MIG for carbon steel duct production.
• Continuous seam welding on a dedicated welder. The SBKJ F350 continuous seam welder is purpose-built for HVAC grease-duct longitudinal seams — automated travel speed, controlled heat input, repeatable weld quality, and certifiable to NFPA 96 / AS 1554.6 weld procedure specifications. A continuous seam welder produces a 1.5 metre seam in a single pass with the same quality every time.

For SBKJ customers fabricating grease duct in volume — a typical Australian commercial kitchen contractor running 1,500 to 4,000 linear metres of grease duct per year — the production answer is an SBAL-V stainless auto duct line for the body forming, an integrated F350 continuous seam welder for the longitudinal seams, and a TIG seam welding station at the bench for short runs, complex transitions and visible finish work. The combined cell can produce 60 to 90 metres of compliant grease duct per shift with two operators.

Clearance to combustibles

NFPA 96 Section 7.7 sets the clearance requirements that drive duct routing and shaft design:

• 18 inches (457 mm) from grease duct surface to combustible construction (timber, gypsum board on combustible substrate, plastic, paper-faced insulation).
• 3 inches (76 mm) from grease duct surface to limited-combustible construction (mineral-wool board with paper face, fire-rated gypsum, magnesium oxide board).
• 0 inches (full contact) when the grease duct is wrapped with a listed grease duct enclosure system installed strictly per the listing, or when factory-built listed grease duct (UL 1978 / FM 4920) is used per its listing.

The listed enclosure-wrap option has transformed Australian commercial kitchen design over the last 15 years. Two products dominate the market:

• 3M FireMaster FastWrap XL — a 1.5 inch (38 mm) ceramic blanket wrapped in two layers, providing a 2-hour fire rating and zero-clearance installation. UL listed under UL 2221 and Intertek listed under ASTM E2336.
• Thermal Ceramics FireMaster Marine Plus — a similar 2-layer ceramic blanket with marine and high-humidity ratings. Common in coastal Australian applications.

The wrap allows the grease duct to penetrate plenum spaces and shafts that would otherwise require 18 inches of clear space, dramatically reducing the architectural footprint of a kitchen exhaust riser. The trade-off is installed cost: a wrapped grease duct system costs roughly 40 to 60 percent more per linear metre than an unwrapped run with adequate clearance, but in tight urban hotel and apartment-podium retail, the wrap is often the only way to comply.

Slope and grease drainage

Hot grease vapour condenses on cool duct walls. The droplets run down the walls under gravity, and if there is no slope back to a designed collection point, they pool at low spots, oxidise, polymerise into a varnish-like coating, and become both a fire load and a structural blockage.

NFPA 96 Section 7.6 requires:

• 1 inch per foot (1:12, or 83 mm/m) minimum slope on horizontal runs under 75 feet (23 metres).
• 2 inches per foot (1:6, or 167 mm/m) minimum slope on horizontal runs over 75 feet.
• All slope must be toward an approved grease reservoir, a listed grease cup, or back to the hood.
• Vertical risers do not require slope, but every horizontal change of direction must be designed to drain.

AS 1668.2 takes a less prescriptive approach and is sometimes referenced as supporting a 1:60 (17 mm/m) minimum on long runs. In practice, when a project is specified to NFPA 96, the higher slope governs — Australian fabricators commonly install at 1:12 or 1:60 depending on which standard the project nominates. For SBKJ customers we always recommend 1:12 minimum because the cost of slope is trivial and the benefit is 20 years of grease drainage performance.

The approved grease reservoir at the low end is typically a stainless cup welded into the duct floor with a removable plug for daily cleaning, or a more sophisticated grease management system such as the Phoenix Solutions or Total Filtration grease collection unit. Either way, the reservoir is part of the daily kitchen cleaning routine — never a set-and-forget detail.

Velocity — the entrainment requirement

The other physical principle behind grease duct design is gas velocity. Grease vapour and droplets must stay in the air stream all the way to the exhaust fan, otherwise they fall out, deposit on duct walls, and increase the cleaning frequency and fire risk.

The NFPA 96 minimums are:

• Horizontal duct: 1,500 ft/min (7.6 m/s) minimum. Below this, grease droplets fall out of the airstream and deposit on the duct floor.
• Vertical duct: 500 ft/min (2.5 m/s) minimum. The lower minimum acknowledges that gravity helps droplet transport in a downward direction (hood-to-roof discharge in most installations).

SBKJ engineering practice tightens both numbers for safety margin — we recommend designing to 4 m/s minimum vertical and 8 m/s horizontal, which gives a 25 to 30 percent buffer against duty cycles where the fan is running at part speed (DCKV demand-control mode) and prevents grease fall-out at low cooking activity. The trade-off is a slightly smaller duct cross-section at design airflow, which actually saves material and weight without compromising safety.

The other direction matters too — maximum velocity. NFPA 96 does not prescribe a maximum, but practical limits are 12 m/s on horizontal and 15 m/s on vertical to keep noise, static pressure and fan power under control. Above 15 m/s the duct sounds like a wind tunnel and the fan motor sizing becomes uneconomic.

Cleanout doors — access at every change of direction

NFPA 96 Section 7.4 requires access doors at every change of direction, at the base of every vertical riser, and at no greater spacing than 12 feet (3.6 m) on horizontal runs. The doors must be:

• Listed for grease duct service — typically UL 1978 or FM 4920 listed. Common brands include Ductmate ULtimate, Cesco Maxi-Vent, 3M Cleanseal and Nordfab QuickSeal.
• Gasketed and grease-tight with a high-temperature silicone or graphite gasket rated for sustained 200 degrees Celsius service.
• Labelled "Access Panel — Do Not Obstruct" in permanent letters at least 25 mm high.
• Located for human access — minimum 600 mm clearance in front of the door, and not more than 2.4 metres above floor without a fixed platform.

The cleaning frequency requirement in NFPA 96 Section 11 is the reason cleanout doors matter so much. Type 1 grease duct must be cleaned to bare metal at intervals based on cooking volume — monthly for high-volume operations like quick-service restaurants and busy hotel banquet kitchens, quarterly for moderate-volume cafes and casual dining, and annually for low-volume operations such as occasional-use ballroom kitchens. Without sufficient cleanout doors, the cleaning crew physically cannot reach every internal surface and the operator falls out of compliance.

Fire suppression integration — Ansul R-102 and equivalents

NFPA 96 Section 10 requires every Type 1 hood to be protected by a UL 300 listed pre-engineered wet-chemical fire suppression system. The system discharges a potassium-acetate-based agent (commonly branded as Wet-Chem, K-Ace or PowderJet) through fixed nozzles aimed at every cooking appliance, the hood plenum, and the vertical duct riser entrance.

The four dominant brands in Australian commercial kitchens:

• Ansul R-102 — the market leader, manufactured by Tyco / Johnson Controls. R-102 is the de facto standard on hotel chains, hospital systems and most international quick-service restaurant brands.
• Pyro-Chem Kitchen Knight II — a Tyco / JCI sister brand to Ansul, common on smaller installations.
• Range Guard — manufactured by Buckeye Fire Equipment, common on independent restaurants and smaller commercial kitchens.
• Amerex KP / Strike — manufactured by Amerex Defense, growing share in Australian hotel and restaurant work.

The interface between the fire suppression system and the ductwork is critical. The duct designer must:

• Provide a flat, square nozzle-mounting location at the base of the vertical riser, typically 600 mm above the hood top, for the duct-protection nozzle.
• Ensure the duct riser is straight for at least 1 metre above the nozzle so the discharge plume can reach the duct interior.
• Coordinate with the suppression contractor on the fusible-link locations — typically inside the hood plenum and at the duct nozzle, with each link rated 165 to 232 degrees Celsius depending on the cooking application.
• Ensure the gas valve interlock and the exhaust-fan interlock are wired so a discharge shuts gas supply and continues exhaust fan operation (NFPA 96 requires the exhaust fan to continue running during and after a discharge to clear the agent and any residual smoke).

The suppression system is not optional and not retrofittable as an afterthought — it must be integrated at the duct design stage because nozzle placement constrains duct geometry. SBKJ engineering teams routinely coordinate with Ansul-certified installers in Australia (Wormald, Chubb Fire & Security, Tyco Australia and Fire Protection Industries) on the duct riser detail before the duct is fabricated.

Make-up air — 80 to 90 percent of exhaust

Every cubic metre of air pulled out through the kitchen exhaust must be replaced. The make-up air (MUA) sub-system is what replaces it, and getting it wrong is the most common comfort and energy failure mode in commercial kitchens.

NFPA 96 and AS 1668.2 both require make-up air at 80 to 90 percent of exhaust airflow, leaving 10 to 20 percent of the kitchen demand to be drawn from the dining or service area. This deliberate negative pressure is what keeps cooking smells inside the kitchen and out of the dining room — get the balance wrong and either the kitchen is in positive pressure pushing smells out, or the kitchen is in such strong negative pressure that the hood capture velocity collapses and smoke spills into the kitchen.

Three MUA strategies:

• Untempered transfer air. The cheapest option — air drawn from the dining room or adjacent conditioned space and transferred through grilles. Acceptable in mild Australian climates (Sydney, Brisbane, Perth) for small kitchens. Fails in Melbourne winter and Cairns summer.
• Direct-fired tempered MUA. A roof-mounted unit with a gas-fired heat exchanger that warms outdoor air to a target supply temperature (typically 18 to 22 degrees Celsius). The standard Australian solution for hotel and quick-service restaurant kitchens. Brands include Greenheck DGX, CaptiveAire A1 and Reznor RHC.
• Indirect-fired or DX-cooled tempered MUA. A more sophisticated unit with both heating and cooling for year-round comfort. Common in hospital and hotel banquet kitchens where staff comfort is a sustained requirement. Adds 30 to 50 percent capital cost over direct-fired heat-only.

The duct fabrication implications are significant. MUA duct is supply-side conditioned air — Type 2 service, galvanised acceptable, mechanical-seam acceptable. The same SBKJ SBAL-V machinery that fabricates stainless grease duct also handles galvanised MUA duct on a separate run, so a single duct fabrication shop can serve both sides of a kitchen exhaust project from the same factory floor.

Demand control kitchen ventilation (DCKV)

The biggest energy story in commercial kitchens over the last 20 years has been the rise of Demand Control Kitchen Ventilation. The principle is straightforward: a typical commercial kitchen runs full-speed exhaust during the entire trading day even though peak cooking activity occupies only 30 to 50 percent of that time. The other 50 to 70 percent of operating hours, the kitchen is exhausting fully-conditioned indoor air to the roof at full fan power for no benefit.

DCKV uses hood-mounted temperature sensors and optical / infrared smoke sensors to detect cooking activity and modulates the exhaust and make-up air fans on variable frequency drives (VFDs). The result is typically:

• 30 to 50 percent of design airflow during idle periods — when no appliance is in use, the system holds at 30 to 50 percent fan speed to maintain hood capture and slight negative pressure.
• 100 percent design airflow during active cooking — the hood ramps up within 30 seconds of detecting heat or smoke at any appliance.
• Annual fan energy savings of 50 to 70 percent — measured against a constant-volume baseline.
• Annual conditioning energy savings of 30 to 50 percent — because reduced exhaust requires reduced make-up air, and the make-up air is the dominant heating and cooling load on a commercial kitchen.
• Payback under three years on most quick-service restaurant and hotel installations.

The four dominant DCKV brands in Australian and international commercial kitchens:

• Halton M.A.R.V.E.L. — Finnish-headquartered global leader. Premium price point, strong installed base on hotel chains.
• Melink Intelli-Hood — U.S.-headquartered, large U.S. installed base. Strong on quick-service and full-service restaurant.
• CaptiveAire DCV — U.S.-headquartered, vertically integrated with their hood and MUA unit lines.
• Spring Air Systems — Canadian-headquartered with Australian distribution, growing share on schools and hospital cafeterias.

The duct design implication of DCKV is the velocity-margin point we made earlier: at 50 percent fan speed the duct velocity drops to 50 percent of design, which can fall below the 7.6 m/s horizontal NFPA 96 minimum. This is why SBKJ recommends sizing horizontal grease duct to 8 m/s at full speed — at 50 percent DCKV setback the duct still holds 4 m/s, which keeps grease droplets entrained on the descending side of the duty cycle.

Listed grease duct versus field-fabricated

The choice between listed factory-built grease duct (UL 1978 or FM 4920) and field-fabricated welded duct is a project-economics question that turns on three variables: building height, riser routing complexity, and labour cost.

Listed factory-built grease duct is a double-wall steel-and-insulation assembly with a UL or FM listing for zero-clearance installation. Brands:

• Van-Packer — the U.S. market leader, double-wall stainless inner with insulated outer. Common on hotel and quick-service restaurant installations.
• DuraVent FasNSeal AL29-4C — a specialised listed grease duct used on commercial kitchen and modular kitchen applications.
• Schebler Chimney Systems — listed grease duct for both food service and industrial venting.
• AmpcoFlue / Selkirk — competitor offerings with similar listings.

The trade-offs:

• Listed duct advantages: Zero-clearance installation (no 18-inch envelope around the duct in the shaft), faster on-site assembly with pre-engineered fittings, single manufacturer warranty across the duct, hangers and fittings, fewer field welds to inspect.
• Listed duct disadvantages: 2 to 3 times the material cost per linear metre versus field-fabricated, restricted to manufacturer's standard fitting geometry (some custom transitions are not listed and require a hybrid approach), longer lead time for non-standard configurations.
• Field-fabricated advantages: Lower material cost, complete custom geometry, faster lead time when fabricated locally, supports Australian fabrication businesses.
• Field-fabricated disadvantages: Requires the 18-inch clearance envelope or a wrapped enclosure, more on-site weld inspections, slower assembly per linear metre.

The practical answer on most Australian projects is hybrid — listed factory-built grease duct on the high-rise vertical riser where shaft space is critical, field-fabricated welded duct on the kitchen-level horizontal runs where geometry is custom and clearance is available. SBKJ supports the field-fabricated side of this hybrid with the SBAL-V stainless duct line for the body forming and the F350 continuous seam welder for the longitudinal seams.

The fan, the discharge, and the roof curb

NFPA 96 Section 8 covers exhaust fans and discharge. The mandatory provisions:

• Upblast exhaust fan listed for grease duty — typically Greenheck CUBE, Cook QMX, Twin City BCRD or Loren Cook QM. The upblast configuration discharges vertically to the sky, away from the building, and includes a grease cup to capture wall-shed grease.
• Discharge minimum 10 ft (3 m) from any property line, parapet, fresh-air intake, operable opening, or pedestrian walkway.
• Discharge minimum 40 inches (1 m) above the roof deck — measured to the highest point of the discharge plenum.
• Hinged on a clamshell base for cleaning access — the fan must be tippable for access to the duct riser top and impeller cleaning.
• Continuous operation during fire suppression discharge — the fan must continue running during and after a wet-chemical discharge to clear the agent, the discharge byproducts, and any residual smoke.

The roof curb under the fan is a detail that is consistently mis-specified. NFPA 96 requires:

• Grease-tight curb with welded or sealed corners — no fastener holes that could pass grease to the roof membrane.
• Drain back to the duct or to a roof-mounted grease containment vessel — never to the roof drainage system.
• Insulated where required to maintain the duct cleanliness temperature gradient.

Roof curb manufacturers common in Australia: Greenheck, Cook, RPS Engineering, and several Australian fabricators including Eastern Sheet Metal and Holyoake.

The Australian commercial kitchen exhaust market

SBKJ engineers spend significant time with the operators who make the largest kitchen-exhaust buying decisions in Australia. Understanding their procurement standards is part of why our Australian customers win those projects, so it is worth mapping the major operator landscape.

Contract catering and food service:

• Compass Group — the largest contract caterer in Australia, operating cafeterias and food services across mining, education, healthcare, business and sports venues. Specifies NFPA 96 grease duct on their corporate-standard kitchen design.
• Sodexo — global contract caterer with significant Australian remote-site, healthcare and corporate presence. NFPA 96-aligned corporate spec.
• ISS Catering — facilities-management caterer with healthcare and education concentration.

Hospital systems:

• Ramsay Health Care — Australia's largest private hospital operator, multi-site standard kitchen specification.
• Healthscope — second-largest private hospital network, standardised kitchen exhaust to NFPA 96 with AS 1668.2 overlay.
• Epworth HealthCare — Victorian private hospital network with strong Melbourne presence — natural alignment with SBKJ's Box Hill North VIC headquarters.
• Public hospital networks — state-by-state procurement: Health Infrastructure NSW, Victorian Health Building Authority, Queensland Health, etc., each with kitchen design standards that reference AS 1668.2 and AS 4674.

International quick-service restaurant chains:

• McDonald's Australia — over 1,000 stores, corporate engineering standard written to NFPA 96 with global brand alignment. Significant remodel and new-build pipeline.
• KFC Australia — Yum! Brands franchise network, NFPA 96 spec for fryer exhaust. Heavy fryer load drives the most demanding grease-duct cleaning frequency.
• Hungry Jack's — Australia's Burger King franchise (independent of the global Burger King brand for the Australian market), NFPA 96 corporate spec.
• Domino's Pizza Enterprises — over 700 Australian stores, conveyor-oven exhaust as Type 1 grease duct because of pepperoni and meat-topping grease load.
• Guzman y Gomez — fast-growing Mexican QSR chain, char-grilled protein lines requiring Type 1 hoods and welded grease duct.
• Mad Mex — competitor Mexican QSR network with similar Type 1 requirements.
• Schnitz — chicken schnitzel QSR with deep-fryer load.
• Roll'd — Vietnamese QSR with wok and char-grilled protein lines.

Hotel groups operating in Australia:

• Marriott International — multi-brand portfolio (Marriott, Sheraton, Westin, W, Le Meridien, Element) — NFPA 96 corporate engineering standard across all banquet, restaurant and room-service kitchens.
• Hilton — multi-brand Hilton portfolio, NFPA 96 corporate spec.
• Accor — French-headquartered global operator with the largest Australian hotel portfolio (Sofitel, Pullman, Novotel, Mercure, Ibis), engineering spec referencing both NFPA 96 and EU EN 1505/EN 1506 with AS 1668.2 local overlay.
• IHG (InterContinental Hotels Group) — Crowne Plaza, Holiday Inn, Indigo, InterContinental — NFPA 96 corporate spec.
• Hyatt — Park Hyatt, Grand Hyatt, Hyatt Regency — NFPA 96 corporate spec, very prescriptive on stainless visible kitchen equipment.
• Crown Resorts — Australian-headquartered casino-hotel operator (Crown Melbourne, Crown Sydney, Crown Perth) — significant restaurant-tenant kitchens, each tenant fitout subject to base-build NFPA 96 grease-duct provision.

The pattern across all of these operators is consistent: NFPA 96 is the prevailing technical specification, AS 1668.2 is the local-code overlay, and the fabrication standard is welded stainless 304 (with 316 in coastal and pool-deck locations). SBKJ's Australian customer base is heavily concentrated in the contractors who fabricate and install for these operators — and the SBAL-V stainless duct line is specifically engineered for this market.

SBKJ machine configuration for commercial kitchen exhaust fabrication

The SBKJ machinery cell that has emerged as the standard solution for Australian commercial kitchen exhaust fabricators is a three-station configuration:

• SBAL-V stainless auto duct line. Full 304 / 316 stainless capability, anti-scratch dual-coil decoiler with PE film protection, hardened forming rollers, integrated coil straightener, automatic notching and shearing, TDF flange forming for Type 2 supply duct (where applicable), and integrated continuous-seam welder station for grease-duct longitudinal seams. Single-shift output 60 to 90 metres of finished grease duct per shift.
• F350 continuous seam welder. A dedicated longitudinal-seam welder built specifically for HVAC duct construction. Automatic travel speed, controlled heat input, repeatable weld quality. The F350 produces a 1.5 m seam in a single pass, full penetration, external bead, NFPA 96 / AS 1554.6 compliant. Pairs with the SBAL-V or operates as a standalone bench welder for off-line work.
• TIG seam welding station. A bench-mounted TIG (GTAW) station for short runs, complex transitions, fittings, and visible-finish work. Argon shielding, autogenous welds on thin gauges, minimal heat input, minimal distortion. Used for the 20 percent of kitchen exhaust duct that is geometry too complex for the continuous welder — reducers, takeoffs, transitions, hood plenums and visible-finish hospital and hotel kitchen runs.

For a typical Australian commercial kitchen contractor running 1,500 to 4,000 linear metres of grease duct per year, the SBAL-V plus F350 plus TIG cell pays back in 18 to 30 months versus an alternative buy-in of welded stainless duct from a sub-contracted fabricator. The headcount required to operate the cell is two skilled operators plus a quality-inspector — comfortably within the staffing model of an Australian sheet-metal contractor.

SBKJ's positioning here is not as a generalist — it is as a stainless-rated, NFPA-96-aware, Australian-supported supplier of the specific machinery needed to fabricate compliant grease duct in volume. The SBAL-V line shares 80 percent of its frame and electrical platform with our SBAL-III galvanised line, but the differences — anti-scratch decoiler, hardened stainless rollers, coil straightener for stainless temper, integrated continuous welder — are exactly the differences that matter for grease-duct fabrication. See our SBAL-V versus SBAL-III comparison for the detailed configuration breakdown.

Inspection, testing and AHJ commissioning

Every NFPA 96 grease-duct installation in Australia is subject to a final inspection by the local Authority Having Jurisdiction (AHJ) — typically the building surveyor and the local fire authority (Country Fire Authority in Victoria, Fire and Rescue NSW, Queensland Fire and Emergency Services). The inspection covers:

• Visual weld inspection. Every longitudinal and transverse weld inspected for full penetration, no porosity, no undercut, no overlap. The AHJ may sample randomly or inspect every weld depending on the project value.
• Clearance verification. All combustible-construction clearances physically measured against the 18-inch / 3-inch / 0-inch (with listed wrap) standard.
• Slope check. Slope measured with a digital level on every horizontal run — typical AHJ tolerance is plus or minus 5 percent of nominal slope.
• Cleanout door access. Every door opened and closed, gasket inspected, label verified.
• Fire suppression discharge test. Live discharge of the wet-chemical agent (dry test using compressed air on the system) to verify nozzle coverage and gas-valve interlock operation.
• Fan rotation and balance. Fan started, rotation verified, balance and vibration measured against ISO 14694 or AS 1851 standards.
• Pressure-leak test. Duct system pressurised to 1.5 inches WG (375 Pa) and held for 5 minutes to verify leak-tightness.

The pressure-leak test is the test most often failed on field-fabricated grease duct. The failure mode is almost always a missed weld — a 50 mm section of un-welded longitudinal seam, a transverse joint that was tacked but not continuously welded, or a cleanout door gasket that was not properly seated. SBKJ recommends a pre-AHJ pressure test by the fabricator on every job, with a hold-and-rectify procedure, before scheduling the formal AHJ inspection. The cost of a re-inspection after a failed test is significantly higher than the cost of a pre-test by the contractor.

Common code-violation failure modes

From SBKJ field-engineering and our customers' rework experience, the five most common NFPA 96 violations in Australian commercial kitchen installations:

1. Pittsburgh-lock seam on grease duct. The single most common violation — a fabricator habituated to Pittsburgh-lock fabrication runs grease duct on the same machine without welding the seam. Detected by AHJ visual inspection at 100 percent failure rate.
2. Galvanised duct in Type 1 service. Often a labelling-error mistake where Type 2 stock is used for what should be Type 1 — detected by AHJ before commissioning, results in complete duct replacement.
3. Insufficient slope. The duct is installed level or with a slight reverse slope toward a low point that is not connected to a grease reservoir. Detected during the slope measurement phase of AHJ inspection.
4. Inadequate cleanout door spacing. A long horizontal run is installed with one cleanout door at each end and no intermediate doors — leaving 5 to 8 metres of duct that no cleaner can physically access. Detected during AHJ inspection or, more commonly, during the first scheduled cleaning.
5. Mis-classified hood. A combination oven or skillet is installed under a Type 2 hood that should be Type 1 — typically detected when the fire engineer reviews the menu and identifies grease-bearing dishes that were not accounted for in the original hood selection. Most expensive failure mode because it requires hood replacement, duct replacement, and fire suppression installation.

The pattern across all five is the same: the violation is detectable at design review, well before fabrication starts. SBKJ's recommendation to our customers is always to involve the fire engineer and the AHJ at the design-review stage, not the commissioning stage — the cost of a one-hour design review meeting is significantly less than the cost of rebuilding non-compliant ductwork.

Maintenance and ongoing compliance

NFPA 96 Section 11 sets the cleaning frequency requirements that an operator must follow over the life of the kitchen. The frequencies are:

• Monthly — solid-fuel cooking operations (wood-fired pizza ovens, charcoal grills) and 24-hour cooking operations (hospital cafeterias, hotel banquet kitchens during major events).
• Quarterly — high-volume cooking operations (quick-service restaurants, busy hotel restaurants).
• Semi-annually — moderate-volume cooking operations (cafes, casual dining).
• Annually — low-volume cooking operations (occasional-use ballroom kitchens, light cooking such as warming and reheat-only).

The cleaning method specified by NFPA 96 is hand-scraping and pressure-washing to bare metal, with the cleaning crew documenting the work with before-and-after photographs of every accessible surface. The cleaning is performed by a certified hood-cleaning contractor — in Australia, members of the Australasian Kitchen Hood and Exhaust Cleaning Association.

The duct fabrication implication is that the duct and its cleanout doors must be designed for cleaning access from day one. Internal smooth surfaces (welded full-penetration seams with the bead external), gasketed cleanout doors at every change of direction, and a slope back to a removable grease cup are the three features that determine whether a duct is cleanable in 2 hours per quarter or 8 hours per quarter — and that ratio determines whether the operator stays in compliance over 10 years.

Putting it all together — the SBKJ engineering checklist

For an Australian commercial kitchen contractor specifying and fabricating an NFPA 96 grease duct system, the engineering checklist is:

1. Confirm hood classification — Type 1 if any grease-bearing appliance is present.
2. Select the governing standard — NFPA 96 (2024) for international brand work, AS 1668.2 Section 6 for local-code-only work, with AS 4674 for food premises always.
3. Specify the duct material — 16 gauge carbon steel for concealed back-of-house, 18 gauge stainless 304 for visible and coastal, 18 gauge stainless 316 for marine and chloride-rich.
4. Specify continuously welded longitudinal seams — F350 continuous seam welder for production, TIG for finish work, MIG only for concealed carbon steel.
5. Specify continuously welded transverse joints — no S-cleat, no TDF flange.
6. Set 18-inch / 3-inch / 0-inch clearance per construction type — coordinate with architectural shaft sizing.
7. Slope at 1:12 minimum toward a designed grease reservoir.
8. Velocity at 7.6 m/s horizontal minimum, 4 m/s vertical SBKJ recommendation — sized at design airflow with DCKV setback margin built in.
9. Cleanout door at every change of direction, every 12 ft horizontal, base of every riser — listed, gasketed, labelled.
10. Fire suppression integration — Ansul R-102 or equivalent, coordinated at duct design stage.
11. Make-up air at 80 to 90 percent of exhaust — direct-fired tempered MUA standard for Australian climates.
12. DCKV controls — Halton, Melink, CaptiveAire DCV or Spring Air, with 3-year payback target.
13. Listed roof exhaust fan, grease cup, and grease-tight curb — Greenheck, Cook or Twin City, with 10 ft clearance from any opening.
14. Pre-AHJ pressure test at 1.5 inches WG (375 Pa) before scheduling the formal inspection.
15. AHJ commissioning inspection — visual welds, clearance, slope, cleanout, fire suppression, fan rotation, leak test.

This 15-step checklist is the same one SBKJ engineers walk through with our Australian commercial kitchen contractor customers when we configure the SBAL-V plus F350 plus TIG fabrication cell. The checklist drives the machinery configuration, the operator training, and the quality-control record-keeping — not the other way round. The machine exists to fabricate compliant duct; the duct does not exist to fit the machine.

Talk to an SBKJ engineer about NFPA 96 stainless duct fabrication →

FAQ

What is the difference between Type 1 and Type 2 commercial kitchen hoods?

Type 1 hoods are listed for grease-laden vapours from cooking appliances such as deep fryers, griddles, charbroilers and ranges. They require welded grease duct constructed of 16 gauge carbon steel or 18 gauge stainless to NFPA 96. Type 2 hoods handle non-grease heat, steam and moisture from dishwashers, ovens and steam kettles — they may use lighter-gauge galvanised duct because no grease residue is present.

What gauge and material does NFPA 96 require for grease duct?

NFPA 96 (2024) Section 7.5 requires 16 gauge (1.5 mm) carbon steel minimum or 18 gauge (1.2 mm) stainless minimum, with continuously welded liquid-tight joints. Galvanised steel and Pittsburgh-lock seams are explicitly prohibited.

How much clearance to combustibles does NFPA 96 require?

18 inches (457 mm) to combustible construction, 3 inches (76 mm) to limited-combustible, or 0 inches with a listed grease-duct enclosure wrap installed per the manufacturer's listing.

What slope and velocity does grease duct require?

1 inch per foot (1:12) horizontal slope minimum toward a grease reservoir; 7.6 m/s horizontal velocity minimum and 2.5 m/s vertical velocity minimum (NFPA 96), with SBKJ recommending 4 m/s vertical for safety margin.

Does Australia follow NFPA 96 or AS 1668.2?

Australian projects typically reference both — fabricate to NFPA 96 weld and material specs, document compliance with AS 1668.2 Section 6 for the local AHJ, meet AS 4674 for food premises hygiene. NFPA 96-compliant duct automatically satisfies AS 1668.2.

What is DCKV demand control kitchen ventilation?

A control strategy that modulates exhaust and make-up air fans on hood-mounted temperature and smoke sensors, running 30–50 percent during idle and 100 percent during cooking. Annual savings 50–70 percent on fan energy, payback under 3 years on most installations.

Why does galvanised duct fail in grease applications?

Galvanised steel loses its zinc coating to dezincification under sustained grease vapour, develops pinhole leaks, and in a fire releases toxic zinc oxide fume. NFPA 96 prohibits galvanised in Type 1 service.

Why does Pittsburgh-lock seam fail NFPA 96?

Pittsburgh-lock is a mechanical folded seam, not welded, not liquid-tight, and not pressure-rated for fire-condition positive pressure. NFPA 96 requires continuously welded longitudinal seams, full penetration, external to the duct, liquid-tight. SBKJ supplies the F350 continuous seam welder and TIG seam welding stations specifically for this requirement.