Commercial Kitchen Ventilation: What You Need Before You Fit Out
Before You Sign the Lease
Most restaurant and cafe fitouts need a mechanical engineer. The exhaust system is not something you sort out later. It drives ceiling height, roof penetrations, duct routes, and make-up air supply. Get it wrong and the certifier will not sign off on your fitout.
Two Australian Standards control the design. AS 1668.1 covers fire and smoke control. It sets the rules for how kitchen exhaust ducts are built, fire-rated, and routed through the building. AS/NZS 1668.2 covers ventilation rates. It tells the engineer how much air to exhaust based on your cooking equipment.
Your council checks the system before you open. Your building certifier checks it against the NCC. Start engineering early. If the duct cannot reach the roof, you may need a different tenancy.
What the Standards Require
- A kitchen exhaust hood is required where any cooking apparatus exceeds 8 kW electric or 29 MJ/h gas, or more than one exceeds 0.5 kW/m². (NCC 2022 F6D12)
- Minimum exhaust rate of 250 L/s per m² of cooking surface. The actual rate depends on the cooking process type and hood configuration. (AS/NZS 1668.2, Section 3)
- Hood overhang of at least 150 mm past the cooking surface for process Types 1 to 4 and 300 mm for Type 5. Woks (Type 6) need 600 mm and Type 7 ovens need 450 mm. AS 1668.2:2024 raises Types 1 and 4 to 300 mm. (AS/NZS 1668.2, Cl 3.4.4 and 3.5)
- Make-up air supply equal to 65–85% of the exhaust flow rate. The remaining air draws in through doors and transfer grilles from adjacent spaces. (AS/NZS 1668.2)
- Outside a dedicated fire-rated shaft, kitchen exhaust ductwork is 1.2 mm galvanised steel or 0.9 mm stainless steel. It also needs an FRL of at least -/60/60. (AS 1668.1:2015, Cl 6.2.3.1)
- Fire dampers are not permitted on kitchen exhaust ducts. Grease would prevent them from closing. (AS 1668.1:2015)
- Cleaning access at every change of direction and no more than 3 m apart (AS 1668.1:2015, Cl 6.2.3.2)
- Kitchen exhaust over 1,000 L/s is an objectionable discharge. It must discharge vertically at 5 m/s or more, at least 6 m from boundaries, intakes and openable windows. (AS/NZS 1668.2:2012, Cl 3.10.3) Under AS 1668.2:2024 the trigger rises to 5,000 L/s where the exhaust is treated.
- Grease filters fitted to every hood over grease-producing cooking. Baffle-type filters are standard for commercial kitchens. (AS/NZS 1668.2)
- Automatic fire suppression for high-risk cooking (char-grilling, wok cooking, deep-frying) (AS 1668.1:2015, Section 6)
Hood Types and Cooking Categories
AS/NZS 1668.2 classifies cooking processes by how much grease, smoke, and heat they produce. The type determines the exhaust rate and the hood design. If you have mixed cooking under one hood, the engineer sizes the whole hood to the worst-case type.
| Cooking Process | Examples | Grease / Heat Output |
|---|---|---|
| Type 1 | Dishwashers, non-grease ovens | Non-grease. Steam and heat only. |
| Type 2 | Griddles, ranges, conventional fryers, kettles, gas ovens | Low grease, medium heat. |
| Type 3 | Electric deep fryers, grooved griddles, hot tops | High grease, low heat. |
| Type 4 | Counter barbecues, gas deep fryers | High grease, medium heat. |
| Type 5 | Salamanders, charcoal and solid fuel cooking | High grease, high heat. |
| Type 6 | Woks | High grease, high heat. |
| Type 7 | Bread ovens, combi ovens | Heat and moisture. |
Woks (Type 6) need the largest hood overhang, 600 mm. Charcoal and solid fuel hoods (Type 5) need their own exhaust system, never shared with grease appliances. A cafe with a combi oven is Type 7. A busy restaurant with woks is Type 6.
The hood itself also has a type. AS/NZS 1668.2 Cl 3.4.2 lists seven hood types: low sidewall, corner, sidewall, island, ventilated ceiling, eyebrow and proprietary. Each configuration has a different capture efficiency, which changes the exhaust rate calculation.
What It Costs
Engineering Design Fees
Kitchen exhaust engineering: $3,000–$8,000. This covers hood sizing, exhaust and make-up air calculations, duct layout, fan selection, fire system coordination, and drawings for the certifier. A simple cafe with one hood sits at the low end. A full restaurant kitchen with multiple hoods, Type 5 cooking, and a long duct run to the roof sits at the high end.
Exhaust System Installation
Hood, ductwork, fan, and make-up air system: $15,000–$50,000+. The biggest cost drivers are hood length and duct run distance to the roof. A ground-floor tenancy with a short vertical run costs far less than a tenancy three levels below the roof.
Fire Suppression
An automatic fire suppression system for the hood and duct adds $5,000–$15,000. This is required for Type 5 cooking and strongly recommended for Type 4. The system uses wet chemical agents that activate automatically when the temperature inside the hood exceeds a set point.
Ongoing Maintenance
Budget for professional duct cleaning every 3–6 months depending on cooking volume. Filter cleaning is weekly. Grease buildup in the ductwork is the number one fire risk in commercial kitchens. Maintenance records are part of your annual fire safety statement.
Who Needs to Know What
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References
- AS 1668.1:2015, The use of ventilation and airconditioning in buildings — Part 1: Fire and smoke control in buildings
- AS/NZS 1668.2:2012, The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings (updated 2024)
- National Construction Code 2022, Volume One, Part F6, Light and ventilation (Clause F6D12)
- AIRAH Best Practice Guideline: Commercial Kitchen Exhaust Management (2022)
- Food Standards Australia, Standard 3.2.3 - Food Premises and Equipment
- NSW Food Authority - Food premises design, construction and fitout guide