Kitchen Extract Systems: How They Work and Why They Need Cleaning

What Is a Kitchen Extraction System?

If you run a commercial kitchen, there is an extraction system working above your cooking line every time the stove is on. Its job is straightforward: pull grease-laden air, steam, and smoke out of the kitchen and push it outside the building. Without it, your kitchen would fill with fumes, your walls and ceilings would be coated in grease, and your staff would struggle to breathe.

The system runs from the canopy hood directly above your cooking equipment all the way up through the ductwork and out to a fan on the roof. Every part of that chain has a role, and every part collects grease over time. Understanding how these components fit together helps you see why regular cleaning is not optional — it is a safety and compliance requirement.

Key Components of a Kitchen Extraction System

Canopy Hood

The canopy (or range hood) sits directly above the cooking equipment. It is the first point of capture for grease, steam, and heat rising from your cooking surfaces. Canopies come in different shapes and sizes depending on your kitchen layout, but they all serve the same purpose: funnelling contaminated air into the system.

Baffle Filters

Inside the canopy you will find baffle filters — stainless steel panels designed to catch grease before it enters the ductwork. They work by forcing the airflow to change direction multiple times, which causes grease particles to separate from the air and collect on the filter surface. These are the most accessible part of the system and should be cleaned frequently.

Ductwork

The ductwork connects the canopy to the exhaust fan. It is the highway for all the air leaving your kitchen. Even with good filters, a percentage of grease vapour passes through and coats the inside walls of the duct over time. This is where the biggest fire risk sits, because grease buildup inside ducts is hidden and easy to forget about.

Exhaust Fan

The exhaust fan — usually mounted on the roof — is what drives the whole system. It creates the suction that pulls air through the canopy and ductwork and pushes it outside. When the fan blades get coated in grease, the fan has to work harder, uses more power, and moves less air. Eventually it can overheat or fail.

Make-Up Air

For every cubic metre of air the extraction system removes, the same amount needs to come back in. That is make-up air. Some kitchens rely on natural openings like doors and windows. Larger operations have a dedicated make-up air unit that brings in fresh, tempered air. Without proper make-up air, the extraction system cannot do its job efficiently, and you end up with poor airflow, back-drafting, and uncomfortable working conditions.

How the System Works

The process is simple in principle. When your kitchen is running, heat and grease rise from the cooking surface. The canopy hood captures this contaminated air. Baffle filters trap the heavier grease particles. The remaining air — still carrying fine grease vapour — travels through the ductwork, pulled along by the exhaust fan, and is expelled outside the building. Fresh make-up air flows in to replace what has been extracted, maintaining air pressure balance in the kitchen.

The system runs constantly while cooking is happening. Over hours, days, and weeks, grease accumulates at every point — on filters, on duct walls, on fan blades, even around access panels and joints.

Why Grease Builds Up and What Happens If You Ignore It

Grease buildup is inevitable in any commercial kitchen. The question is not whether it will happen, but how quickly — and that depends on how much you cook, what type of cooking you do (deep frying produces far more grease than steaming), and how well your filters are maintained.

When grease builds up unchecked, the consequences are serious:

• Fire risk: Grease is fuel. A buildup inside your ductwork is effectively a fire hazard running through your building. A kitchen flare-up can ignite grease in the duct and spread the fire well beyond the kitchen.
• Poor air quality: A clogged system cannot move air properly. Your kitchen gets hotter, stuffier, and less comfortable for staff. Smoke and odours linger instead of being extracted.
• Higher energy costs: When airflow is restricted, the exhaust fan works harder to compensate. That means higher electricity bills and faster wear on your equipment.
• Compliance failures: In New Zealand, commercial kitchen extraction is a specified system that requires regular inspection. If your system is dirty or unmaintained, you risk failing your BWOF inspection and facing council enforcement.

Signs Your System Needs Attention

You do not always need to climb on the roof to know your extraction system needs a clean. Watch for these warning signs:

• Visible grease dripping from the canopy or filters
• Smoke lingering in the kitchen during cooking
• Unusual or excessive noise from the exhaust fan
• Grease stains on walls and ceilings near the cooking area
• Staff complaints about heat, odours, or poor airflow
• It has been more than six months since your last professional clean

How Professional Cleaning Works

A proper kitchen extraction clean covers the entire system from canopy to fan. At Ductflow, our process starts with a full inspection and before photos. We then strip and degrease the canopy, remove and clean the filters, work through the ductwork section by section, and clean the exhaust fan and motor. Everything is photographed after cleaning, and you receive a full compliance report documenting the work.

This is not a surface wipe. It is a thorough, systematic clean designed to reduce fire risk, restore proper airflow, and give you the documentation you need for your 12A inspection and BWOF. You can learn more about our process on the kitchen extract cleaning page.