An Australian commercial kitchen needs a mechanical exhaust hood once its cooking appliances pass 8 kW electrical or 29 MJ/h of gas, and the published guideline figure for airflow is 380 litres a second for every square metre of cooking surface.
Skai Solutions answers the phone for restaurants, cafes and takeaways in Australia and New Zealand, so the operators we talk to are usually mid-fit-out and getting a canopy quote they cannot read. Every page that ranks for this query is selling canopies. This one is written from two published sources instead: a council's own hood guideline, which gives the thresholds and dimensions in plain numbers, and an engineering firm's account of what the 2024 revision of AS 1668.2 changed. Where a figure is not public, this page says so rather than inventing one.
At a threshold, and the threshold is lower than most people guess. The City of Wanneroo's published exhaust hood guidelines require a hood if any one of these is true:
Eight kilowatts is one six-burner induction top, or a two-group espresso machine next to a salamander and a panini press. Which is how a small cafe that thought it was doing sandwiches ends up needing mechanical exhaust. The fourth bullet matters as much as the first three: the council has discretion, and it uses it.
Underneath all of it sits the legal floor. Food Standards Code Standard 3.2.3, Food Premises and Equipment, requires food premises to have enough natural or mechanical ventilation to effectively remove fumes, smoke, steam and vapours. That is the obligation. The standard and the council guidelines are how you prove you have met it.
Dimensions, not opinions. Wanneroo publishes these, and they are the ones a plan assessment checks.
| Requirement | Published figure |
|---|---|
| Lowest front edge above floor level | At least 2,000 mm |
| Grease gutter inner edge beyond the appliance perimeter | At least 150 mm |
| Grease filter above a charcoal or open fire | 1,350 mm minimum |
| Grease filter above a naked flame | 1,050 mm minimum |
| Grease filter above a fixed plate or electronic appliance | 600 mm minimum |
| Top of canopy below the ceiling, if not sealed through it | At least 150 mm |
| Filter face angle from vertical | No more than 30 degrees |
| Internal canopy surfaces from vertical | No more than 40 degrees |
Read the three filter heights together, because that is the design decision nobody explains. Moving from a fixed plate to a naked flame pushes the filter line up by 450 mm. Moving to charcoal pushes it up another 300 mm. A ceiling that comfortably fits a griddle canopy may not fit a charcoal grill canopy at all, and that discovery after the slab is poured is an expensive one. If you are pricing a build, our cafe fit-out cost page has what the rest of it runs to, and commercial kitchen equipment cost covers the appliances that drive the kilowatt total in the first place.
Wanneroo's published figure is 0.38 cubic metres a second for every square metre of cooking equipment top surface area, which is 380 litres a second per square metre. Discharge velocity at the outlet must be at least 5 metres a second.
Work a real canopy. A cooking line 2.4 metres long and 0.9 metres deep is 2.16 square metres of top surface, so about 821 litres a second, which is roughly 2,956 cubic metres an hour. That is the number that sizes the fan, the ductwork and the make-up air, and it is why the canopy is rarely the expensive part of the job.
Make-up air is the half that gets skipped. Wanneroo requires at least 10 complete air changes an hour by mechanical supply, or permanent natural ventilation. Pull 821 litres a second out of a sealed room and the exhaust fan fights the door, the gas appliances misbehave, and the dining room gets the kitchen's air pulled through it. Where the air goes out matters too: at least 1 metre above a pitched roof ridge or 3 metres above a flat roof, and at least 6 metres from any property boundary and from any fresh air intake.
Then there is the part that recurs forever. Internal ductwork must be cleaned at least every six months, with grease-tight clean-outs every 3 metres and near every elbow, angle or junction on horizontal runs, and the exhaust must run whenever cooking or heating is happening. Our page on kitchen exhaust cleaning cost has what that six-monthly visit is priced at, and running the fan all service is a real line on your restaurant electricity cost.
Enough that an old canopy design cannot simply be reused. The engineering consultancy Norman Disney and Young set out the differences against the 2012 edition, and these are the ones that bite a hospitality fit-out:
The reclassification is the quiet one. If your appliance changed process type, its required hood type and its flow rate changed with it, even though the appliance on your floor is the same metal box it was last year. NDY's own instruction is that flow rates be worked out again rather than carried over from the old design.
Three honest gaps, because pretending they are not there is how operators get surprised.
The council guides are older than the standard. The Wanneroo document used throughout this page cites AS 1668.2-1991. The standard has been revised twice since. Its thresholds are useful, published and checkable, and they are the council's own guideline, but they are not the current standard and a mechanical engineer will design to the current one.
The 2024 flow rates are not free. NDY says Type 1 and Type 4 hoods may need increased flow and Type 7 rates may reduce, without publishing values. The numbers live inside a paid standard. Nobody writing a page like this can give them to you, and anyone who does without citing the standard is guessing.
Capture velocity has no public number. Wanneroo requires a uniform capture velocity and gives no figure for it. That is a design judgement, which means two engineers can specify two different fans for the same kitchen and both be compliant.
Ventilation and suppression get sold together and are not the same obligation. What the National Construction Code actually requires over a cooking line, and who really makes you fit it, is on whether a fire suppression system is required in a commercial kitchen.
Anyone about to build. This is the map, not the drawing. If you are fitting out, you need a mechanical services engineer working to the current AS 1668.2 and a council plan assessment before anything is ordered, because the cost of a canopy that fails assessment is not the canopy, it is the four weeks of trading you lose waiting for the second one.
Use this page for three things instead: to work out early whether your appliance list crosses 8 kW and therefore whether you need mechanical exhaust at all, to sanity-check the ceiling height against the filter heights before you sign a lease, and to know what the six-monthly duct clean commits you to. Beside it, our page on how many toilets a cafe needs covers the other building requirement that decides whether a tenancy is usable, and pest control requirements covers the annual obligation that an inspector checks at the same visit.
Skai Solutions answers the phone for restaurants, cafes and takeaways in Australia and New Zealand. It has nothing to do with your ductwork. It matters on the day your exhaust fan dies mid service and the phone will not stop while you are on hold to a mechanical contractor. If your phone mostly carries enquiries rather than bookings or orders, a basic message-taking plan is the right buy and it is not us.
When does a commercial kitchen need an exhaust hood in Australia?
The City of Wanneroo's published guideline requires a hood if cooking appliances total more than 8 kW electrical input, or 29 MJ/h of gas, or exceed 0.5 kW per square metre of kitchen floor area (1.8 MJ per square metre for gas), or if the local government decides one is appropriate. Eight kilowatts is reached by a small cafe line more often than operators expect.
How much air does a commercial kitchen exhaust hood have to move?
Wanneroo's published figure is 0.38 cubic metres a second per square metre of cooking equipment top surface, which is 380 litres a second per square metre, with a discharge velocity of at least 5 metres a second. A cooking line 2.4 m by 0.9 m is about 821 litres a second.
How high above the cooktop does the filter have to sit?
It depends on the heat source. Wanneroo's guideline sets a minimum of 1,350 mm above a charcoal or open fire, 1,050 mm above a naked flame and 600 mm above a fixed plate or electronic appliance. The lowest front edge of the canopy must also be at least 2,000 mm above the floor.
What changed in AS 1668.2 in 2024?
According to the engineering consultancy Norman Disney and Young, minimum front and side overhang for Type 1 and Type 4 hoods rose from 150 mm to 300 mm, the maximum horizontal setback for Type 1 fell from 300 mm to 150 mm, Type 7 side overhang dropped from 450 mm to 300 mm, and several appliances were reclassified between process types, which changes their required hood and flow rate.
How often does commercial kitchen ductwork need cleaning?
Wanneroo's guideline requires internal ductwork to be cleaned at least every six months, with grease-tight clean-outs every 3 metres and near each elbow, angle or junction on horizontal duct runs. Filters are to be removed and cleaned often enough to stay clean at all times.
Do I need make-up air as well as exhaust?
Yes. Wanneroo requires at least 10 complete air changes an hour by mechanical supply, or permanent natural ventilation. Exhausting several hundred litres a second from a sealed kitchen without replacing it starves gas appliances, makes doors hard to open and pulls kitchen air through the dining room.