A kitchen can have a high-capacity extraction fan and still fill with heat, steam and cooking fumes. The usual reason is not a single failed component. When customers ask what causes poor extraction, the answer is normally a mismatch between the cooking load, canopy design, duct route, fan duty and make-up air available on site.
Poor extraction affects more than comfort. It can leave grease on ceilings and equipment, make the kitchen uncomfortably hot, create odours in customer areas and increase fire risk within grease-laden ductwork. It may also make it harder to meet the ventilation expectations that apply to commercial kitchens. Finding the real cause early prevents money being spent on a larger fan that does not solve the underlying airflow problem.
What Causes Poor Extraction? Start With Capture
Extraction starts at the canopy, not at the fan. Before air can be removed through ductwork, the canopy has to capture the heat plume, vapour, smoke and airborne grease rising from the cooking equipment. If that plume escapes into the room, increasing fan speed may improve matters slightly but will not produce reliable results.
A canopy that is too short, too narrow or mounted too high above the appliances is a common cause of weak capture. The canopy should project beyond the cooking line sufficiently to contain the rising plume, especially around high-output equipment such as chargrills, woks, fryers and solid-fuel appliances. A compact canopy over a long cooking suite is rarely a cost saving once the kitchen is in use.
The layout matters just as much. Appliances near an open edge are more exposed to cross-draughts, while a busy pass, open door or supply-air grille can push fumes away from the filters. Island canopies need particular care because all sides are exposed. Wall-mounted canopies generally benefit from the wall acting as a barrier, but they still need correct dimensions and a suitable overhang.
Filter condition also affects capture and airflow. Grease filters that are blocked, damaged or poorly fitted create resistance, reduce the volume of air moving through the system and allow grease to bypass where gaps are present. Filters are a working part of the system, not an accessory to clean when time allows.
The Fan Is Often Specified for the Wrong Duty
A fan’s quoted airflow figure can be misleading if it is considered in isolation. A fan may be advertised at a high volume, but that figure is often measured with little or no resistance. Once it is connected to filters, duct bends, transitions, attenuators, discharge louvres and an ESP unit, the available airflow falls.
The fan must therefore be selected against the system’s total static pressure, not simply the canopy size. An undersized fan will struggle from day one. A fan that is physically large but poorly matched to the pressure requirement can also be inefficient, noisy and unable to deliver its intended duty.
Fan rotation, belt tension and motor condition should be checked during fault finding. On belt-driven units, a worn or slipping belt reduces performance without necessarily stopping the fan. Backward rotation following electrical work, a clogged inlet, damaged impeller or failed variable-speed control can have the same practical result: air appears to be moving, but not in the volume required.
Noise is not proof of performance. A loud system may be working against excessive resistance, while a quiet system may simply be underpowered. Proper airflow and pressure testing gives a far clearer picture than judging the installation by sound alone.
Ductwork Resistance Steals Airflow
Ductwork is where many otherwise capable systems lose performance. Every metre of duct, bend, branch, reduction and fitting adds resistance. A long route with repeated sharp elbows can require significantly more fan pressure than a direct, well-designed run.
Undersized ductwork is particularly damaging. It forces air to travel too quickly, increasing pressure loss, noise and grease deposition. Oversized ductwork is not automatically better either, as air velocity can become too low to carry grease-laden air effectively through the system. The duct size, airflow rate and fan pressure must work together.
Poor fabrication and installation can introduce further losses. Flexible ducting used where rigid galvanised or stainless steel ducting is required, badly sealed joints, abrupt changes in duct size and poorly positioned branches all undermine performance. In commercial kitchen extraction, grease-tight ductwork and practical access for cleaning are central to a dependable installation.
The discharge point deserves attention too. If extracted air is released too close to air intakes, opening windows or neighbouring properties, it can be drawn straight back into the building or create odour complaints. A restricted external grille, blocked louvre or poorly placed weather cowl adds resistance at the final stage of the route.
Missing Make-Up Air Creates Negative Pressure
An extraction system cannot remove large volumes of air indefinitely unless replacement air can enter the building. This is one of the most overlooked causes of poor extraction in commercial kitchens.
When there is insufficient make-up air, the kitchen becomes negatively pressurised. Doors become difficult to open, fumes spill from the canopy edges and the fan works against a vacuum. Staff may respond by opening a rear door or window, but uncontrolled incoming air can create a cross-draught that pulls the cooking plume away from the canopy.
A planned fresh-air supply is the better solution. The supply air volume, location and velocity need to be considered alongside the extract system. Air delivered directly into the capture zone at excessive speed can disrupt the plume. Air introduced too far from the kitchen may not relieve pressure where it is needed. In colder months, untreated make-up air may also make the kitchen uncomfortable and encourage staff to shut vents or doors that the system relies on.
The right balance depends on the premises, cooking equipment and operating pattern. A small café kitchen has different requirements from a high-volume restaurant or production facility. This is why a site assessment is more valuable than choosing a fan from a catalogue by airflow alone.
Cooking Equipment Can Outgrow the Original System
Commercial kitchens change. A site may begin with ovens and a modest fryer, then add a chargrill, extra fryers or a higher-output cooking line as trade grows. The extraction installation is often left unchanged.
Different appliances produce very different heat and contaminant loads. Steam from boiling pans, grease aerosol from frying, smoke from grilling and combustion products from gas equipment each place their own demands on capture and extraction. Solid-fuel cooking requires especially careful design because of the heavier particulate and fire considerations involved.
The issue is not only what is installed, but how it is used. A system may cope during preparation yet fail at peak service when every appliance is operating. Assessing the full cooking duty, including the busiest periods, provides a realistic basis for sizing and design.
Maintenance Problems Build Up Gradually
Extraction failure is often gradual. Grease builds inside filters, ductwork and fan impellers, reducing free area and altering the fan’s efficiency. A system that once performed well can become noticeably weaker over several months of heavy use.
Cleaning schedules should match the cooking risk and operating hours. High-grease applications need more frequent attention than light-duty operations. Filters require regular cleaning, while ductwork, fans and associated components need periodic professional inspection and cleaning. Records are useful not only for operational control but also for demonstrating that the system is being properly managed.
ESP units can be highly effective where grease and smoke control is required, but they are not fit-and-forget equipment. Collection cells, pre-filters and electrical components need cleaning and maintenance to operate as intended. A neglected ESP can add resistance to the system and reduce overall extraction performance.
Diagnose the Whole System Before Replacing Parts
A practical inspection follows the airflow path: cooking equipment, canopy, filters, ductwork, fan, air supply and discharge point. Look for visible smoke escape, greasy filter banks, damaged belts, obstructed grilles, poorly sealed duct joints and doors pulling hard under negative pressure. These signs help identify whether the problem is capture, airflow volume, resistance or replacement air.
For reliable answers, measure airflow and static pressure at key points. The results can show whether the fan is underperforming, whether the duct route is too restrictive or whether a component such as a filter bank or ESP is causing an excessive pressure drop. This evidence supports a targeted repair, adjustment or upgrade instead of guesswork.
At CanopyMan, custom-built extraction canopies, ductwork and fan solutions are designed around the actual site, cooking line and discharge route. That approach matters because a premium-quality component only performs properly when it forms part of a balanced system.
If your kitchen feels hotter, smokier or greasier than it should, treat it as an operational warning rather than a nuisance to work around. A properly assessed extraction system protects staff comfort, equipment condition and day-to-day service long before the problem becomes a costly shutdown.