The number people get wrong
The figure quoted in the trade is often 3 MJ/h per m³. That is the limit for flueless appliances. A rack oven that takes its combustion air from the room and sends the products up a flue is open flued, and the trigger is 0.4 MJ/h per m³. Used by mistake, the wrong figure says no extra ventilation is needed at all.
The two pathways
| Pathway | What it requires |
|---|---|
| Natural | Permanent opening direct to outside, 450 mm² of effective free area per MJ/h (Table 6.4.6.2). Effective means after louvre blades and insect mesh, so the louvre face is roughly twice the calculated area. |
| Mechanical | 0.3 L/s per MJ/h for forced draught burners (Table 6.4.9), delivered at low level, at or below burner level, with the Clause 6.4.10 interlock that senses actual air movement and fails safe. |
Flue gas leaves the room too
The products going up the flue are room air. Counting them in the air balance is what keeps the room from going too negative once the hoods, the ovens and the doors are all working at once.
Who does what
The mechanical engineer sets the airflows, the openings, the position of the supply and the control logic. The licensed gasfitter installs and certifies the gas work, including flues and the isolation arrangement. Where an imported oven has no Australian certification, its approval route is a question for Building and Energy before it is connected, and that can take weeks, so raise it early.
Editions matter here: WA has required AS/NZS 5601.1:2022 for new installations since 30 March 2023, and the clause numbers moved between editions. Quote the edition with the clause.
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Send your equipment listQuestions
When do gas ovens need extra ventilation air in a commercial kitchen?
For open flued appliances in a room, AS/NZS 5601.1:2022 Clause 6.4.6.3.1 divides gas input by room volume. Above 0.4 MJ/h per m3, additional ventilation is required: either a permanent opening direct to outside at 450 mm2 of effective free area per MJ/h, or a mechanical supply at low level with an interlock that shuts the gas if the air supply fails. The 3 MJ/h per m3 figure often quoted is the flueless limit, not the open flued one.
Does the make-up air fan have to be interlocked with the gas?
Where the mechanical supply is the pathway the appliances rely on for air, yes. AS/NZS 5601.1:2022 Clause 6.4.10 requires an interlock that senses actual air movement and fails safe, so the gas shuts off when the supply fails. The engineer specifies the logic and the licensed gasfitter installs and certifies the gas side.
More memos
General guidance, not a design. Clause references are to AS 1668.2-2012 with Amendments 1 and 2 (called up by NCC 2022) and AS/NZS 5601.1:2022; NCC 2025 calls up AS 1668.2:2024, where numbering and some values differ, so confirm the edition with your building surveyor. I do the design and calculations as a mechanical engineer (MIEAust); the mechanical contractor installs, commissions and certifies, and a licensed gasfitter certifies gas work. More: kitchen exhaust and ventilation design in Perth · all design memos