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
- 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 beyond the edge of the cooking surface for cooking process Types 1–4, and 300 mm for Type 5 (AS/NZS 1668.2, Appendix E)
- 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)
- Kitchen exhaust ductwork built from 1.2 mm galvanised steel or 0.9 mm stainless steel (AS 1668.1:2015)
- 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 at 3 m intervals on horizontal runs (AS 1668.1:2015)
- Kitchen exhaust over 1,000 L/s must discharge vertically through the roof. Treated exhaust pathways are now available under the 2024 revision. (AS/NZS 1668.2:2024)
- Grease filters fitted to all exhaust hoods. 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 | Boiling, simmering, steaming, poaching | Light duty. Low grease, low heat. |
| Type 2 | Baking, roasting in enclosed ovens | Light duty. Low grease, medium heat. |
| Type 3 | Griddles, ranges, gas ovens, tilting skillets | Medium duty. Medium grease, medium heat. |
| Type 4 | Deep fryers, pasta cookers | Heavy duty. High grease, medium heat. |
| Type 5 | Char-grilling, wok cooking, salamanders, open-flame cooking | Extra heavy duty. High grease, high heat. |
Type 5 cooking needs the most exhaust air, the largest hood overhang (300 mm minimum), and fire suppression. A small cafe with a sandwich press and a bain-marie sits at Type 1–2. A busy restaurant with woks and a charcoal grill is Type 5.
The hood itself also has a type. AS/NZS 1668.2 Appendix E covers seven hood configurations: wall-mounted canopy, island canopy, corner-mounted, low sidewall, and ventilated ceiling among them. 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 F4 — Light and ventilation
- 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