A commercial kitchen ventilation system is more than a fan in a hood. It is a sequenced sub-system — exhaust, make-up air, fire suppression, gas isolation — and the electrical interlocks decide whether the kitchen runs safely or limps along with workarounds.
Hood, fan, make-up — three speeds, one logic
- Exhaust fan starts first to establish negative pressure at the hood
- Make-up air fan follows, balancing the room so the kitchen is not under-pressured against the dining area
- Both fans run on variable speed where the hood is variable-speed; otherwise stepped (low / high)
- Hood lighting hardwired into the same circuit so the user knows the hood is energised
Gas isolation interlock
In gas-fired kitchens, the gas safety solenoid valve is interlocked with the exhaust fan. If the exhaust fan stops or the airflow switch detects loss of flow, the gas valve closes within seconds. The interlock is wired, not software-only, and tested at commissioning. The fire-suppression system on the hood has its own interlock that cuts both gas and electrical supply on activation.
Fire and detection coordination
Most commercial kitchens have hood-mounted fire-suppression (wet chemical), smoke detection coordinated with the building fire alarm panel, and emergency stop buttons accessible from the dining side. The wiring for these systems is the fire-protection contractor's scope, but the electrical contractor supplies clean power, dedicated circuits, and the panel coordination. SCDF interface requirements decide the panel type.
Dedicated equipment circuits
- Combi oven, induction range, fryer — each on its own circuit, sized to the nameplate plus margin
- Refrigeration / cold room — independent circuits per unit; no shared circuits across cold storage
- Dishwashing equipment — dedicated DP isolator, RCD-protected
- Hood lights and exhaust fan — interlocked but separately fusible for maintenance
- GPO sockets for small appliances — multiple circuits so one trip does not stop service
Commission the interlocks, do not assume them
On every kitchen handover we open the hood, kill the airflow switch, and watch the gas valve close. If it does not close in the published time, we re-tune the interlock before the tenant takes over. This step takes ten minutes and prevents the worst kitchen incidents.