A commercial kitchen can have a premium extraction canopy and a powerful fan, yet still struggle with heat, smoke and grease if the duct route is poorly planned. Effective kitchen hood ducting design is what carries contaminated air away from the cooking line, protects the working environment and helps the whole extraction system perform as specified.
The ductwork is not a secondary detail to be fitted around other services at the end of a project. Its size, route, material, access and discharge position should be considered alongside the canopy, cooking equipment and make-up air from the start. Get those decisions right and the result is cleaner air, easier maintenance and a system built for demanding service.
Start Kitchen Hood Ducting Design at the Cooking Line
The cooking appliances determine the extraction challenge. A light-duty preparation area does not create the same heat, grease and plume behaviour as a bank of chargrills, fryers, woks or solid-fuel equipment. The canopy must be sized and positioned to capture the plume effectively before duct dimensions and fan duty can be finalised.
A canopy that is too small, mounted too high or poorly located over the appliances will allow fumes to spill into the room. Increasing fan speed may not solve this problem. It can increase noise, energy use and negative pressure while still failing to capture the rising plume properly. Good extraction begins with capture at source, then moves through a duct system designed to preserve that performance.
The expected airflow volume should reflect the appliance load, canopy arrangement, cooking method and operating conditions. A professional survey also considers ceiling height, nearby doors, pass-throughs and cross-draughts from supply air. These factors affect how the plume behaves and whether the kitchen remains comfortable for staff.
Size Ductwork for Airflow, Not Available Space
Ductwork that is undersized creates unnecessary resistance. The fan has to work harder to move the required volume of air, which can lead to excessive noise, higher running costs and poor canopy capture. In grease-laden systems, high velocities can also carry grease further through the ductwork, increasing the maintenance burden.
Oversized ductwork is not automatically the answer. It can add cost, take up valuable ceiling space and make it harder to achieve suitable air movement through the system. The right duct size is a calculated balance between airflow volume, velocity, pressure loss, grease transport, acoustic control and the physical limits of the building.
Round ducting is often efficient for airflow, while rectangular ducting may be necessary where headroom is restricted or where it must pass through a defined service zone. Both can work well when properly specified. What matters is maintaining adequate free area and avoiding awkward transitions that restrict airflow.
Keep the route short, direct and accessible
Every metre of duct, bend, branch, transition and damper adds resistance. A straight vertical route is generally preferable where the building allows it, but many commercial sites require ductwork to travel through ceilings, risers or external elevations before reaching a safe discharge point.
The practical aim is to create the shortest workable route with the fewest directional changes. Where bends are needed, long-radius bends are normally preferable to tight elbows because they create less turbulence and pressure loss. Abrupt reductions, poorly formed offsets and unplanned flexible connections can all compromise the system.
Access is equally important. Grease extraction ductwork requires regular cleaning, so access panels must be positioned at practical intervals and at changes of direction. If a contractor cannot reach the internal surfaces safely and thoroughly, the duct system has not been designed for long-term operation.
Specify Materials Built for Grease Extraction
Commercial kitchen extraction ducting must withstand heat, grease, cleaning processes and continual use. High-grade stainless steel is a strong choice for visible runs and demanding environments because it is durable, hygienic and resistant to corrosion. It also presents a professional finish where ductwork is exposed.
The construction details matter as much as the sheet material. Duct sections should be suitably sealed and joined to minimise grease leakage. Supports must be correctly designed for the duct weight, particularly where long vertical sections, external runs or heavy-duty filtration equipment are involved.
For grease-laden air, the duct system should be designed as a cleanable, fire-conscious installation rather than ordinary ventilation. Requirements can vary according to the building, cooking risk, landlord conditions, local authority expectations and the applicable UK standards. A site-specific design review is the sensible route, especially for high-output cooking operations or complex buildings.
Plan for fire safety and cleaning from day one
Grease deposits are not simply a hygiene issue. They can reduce airflow, create odours and increase fire risk. Filters in the canopy are the first line of defence, but they do not remove the need for a duct route that can be inspected and cleaned properly.
The system should allow grease to drain or collect in controlled areas rather than escape through joints or gather in inaccessible low points. The discharge arrangement, fan position and any filtration stages should also be chosen with future maintenance in mind.
Where ductwork passes through compartments, ceilings or building elements with fire-resistance requirements, the design needs careful coordination. Do not assume a standard detail is suitable for every project. The extraction route must be assessed alongside the building layout, fire strategy and relevant approvals.
Match the Fan to the Real System Resistance
Fan selection should be based on the completed duct system, not a rough airflow figure alone. The selected fan must overcome the total system resistance created by the canopy, filters, duct length, bends, transitions, attenuators, ESP units and discharge components while delivering the required duty.
An incorrectly selected fan can cause persistent problems. A fan with insufficient pressure capability will not maintain airflow once filters become loaded or the system sees normal operating resistance. An oversized fan may create excessive noise, draughts and energy consumption.
Variable-speed control can provide useful flexibility where cooking demand changes throughout the day. It allows the extraction rate to be adjusted during quieter periods, provided the system still maintains safe and effective capture. This should be a controlled design decision, not a shortcut for an inadequately sized system.
Noise also deserves attention early. Fan noise can travel through ductwork and affect the kitchen, neighbouring premises or nearby accommodation. Fan location, duct velocity, acoustic treatment and discharge position all influence the final result. Solving noise after installation is usually more expensive than designing it out at the start.
Do Not Ignore Replacement Air
Every litre of extracted air needs to be considered in the wider ventilation strategy. If a kitchen removes a large volume of air without sufficient replacement air, doors become difficult to open, cold draughts develop and the canopy may struggle to capture fumes consistently. Gas appliances can also require particular care because combustion air and room pressure conditions matter.
Replacement air should be introduced in a way that supports, rather than disrupts, the capture zone. Blowing high-velocity supply air directly across the front edge of a canopy can push fumes into the room. A balanced approach, with appropriately distributed supply air, helps create a more stable working environment.
This is where a full-system approach pays off. The canopy, ductwork, fan, filtration and supply air arrangement should be treated as one engineered package rather than separate purchases.
Choose the Discharge Position Carefully
The duct termination point affects odour control, neighbour relations, planning considerations and system performance. Discharging close to windows, air intakes, public areas or neighbouring properties can create avoidable complaints, even when the extraction equipment itself is functioning correctly.
The route must be assessed for the building and its surroundings. In some sites, odour-control equipment such as electrostatic precipitators and suitable secondary filtration may be necessary to manage emissions before discharge. These units require correct sizing and planned maintenance, so they should be integrated into the original design rather than added as an afterthought.
External ductwork also needs to withstand the British weather. Suitable materials, weatherproof joints, secure supports and well-considered access arrangements will protect performance and appearance over time.
Build for Installation, Service and Future Change
A technically sound drawing still needs to work on site. Existing beams, electrical containment, sprinkler systems, ceilings and restricted access can all change the installation approach. Early surveying prevents costly alterations once fabrication has started.
Custom manufacture is particularly valuable where standard duct sizes and off-the-shelf components do not suit the building. CanopyMan designs and fabricates premium-quality stainless steel extraction systems around the actual site conditions, helping contractors and operators avoid compromises that affect airflow or maintenance access.
Before sign-off, confirm that the system includes the right access doors, supports, insulation where required, control equipment and commissioning provisions. Airflow testing and balancing should verify that the installed system achieves the intended extraction duty, not simply that the fan is running.
A well-planned duct system is rarely the most visible part of a commercial kitchen, but staff notice its effect every shift. Design it around the cooking load, the building and the service needs of the operator, and the extraction canopy will have the support it needs to do its job properly.