Poor extraction rarely starts at the fan. More often, it begins with ductwork that is too small, too long, full of sharp turns or difficult to clean. These duct layout planning tips help commercial kitchen operators, facilities managers and contractors design extraction routes that move air properly, support compliance and remain practical to maintain.
A duct system is not simply a connection between an extraction canopy and an outlet. It is a working part of the ventilation system. Its route, size, materials and fittings all affect airflow, noise, energy use and the ability of the system to capture heat, steam, smoke, fumes or airborne contaminants where they are produced.
Start With the Process, Not the Duct Route
The first question is not where the duct can fit. It is what the extraction system needs to remove and how much air it must move. A busy commercial kitchen line producing grease-laden vapour needs a different approach from a welding bay, bakery, woodworking workshop or general production area.
Identify the source of contaminants, the equipment operating at the same time, the expected duty cycle and the capture point. For a kitchen, this means considering the cooking appliances beneath the extraction canopy, their heat output and the likely plume direction. In a factory or workshop, it means establishing whether contaminants need source capture, general extraction or both.
This early assessment determines the required airflow volume. Once that figure is known, the duct can be sized to maintain suitable transport velocities without creating unnecessary pressure loss. Choosing duct dimensions before calculating airflow is a common and expensive mistake.
Keep Duct Runs Short, Direct and Purposeful
Every metre of ductwork creates resistance. Every elbow, branch, transition and grille adds more. The most efficient route is usually the shortest practical route from the extraction point to the discharge location, with as few direction changes as the building allows.
That does not mean forcing a straight line at all costs. A route still needs safe clearances, access for cleaning, appropriate structural support and a sensible discharge position. It may also need to avoid rooflights, electrical services, fire compartments or occupied neighbour-facing areas. Good planning balances low resistance with buildability.
Where a turn is unavoidable, use smooth-radius bends rather than abrupt square elbows wherever the application permits. A sharp change in direction disrupts airflow and increases system resistance. Several poor fittings in one run can leave even a correctly specified fan struggling to deliver its design duty.
Avoid unnecessary offsets
Offsets are sometimes unavoidable when working around beams, ceilings and existing services. Keep them to a minimum and make each one earn its place. A compact route with two well-designed bends is generally better than a long run that zig-zags through the building just because there is nominal space available.
Measure the actual site, not only the drawings. Older premises and refurbishment projects often reveal hidden services, changed ceiling levels and structural details that affect the proposed route.
Size Ductwork for Airflow and Pressure Loss
Duct size has a direct effect on system performance. Undersized ductwork drives air velocity up, raising resistance, noise and fan energy demand. Oversized ductwork can be harder to accommodate, cost more and, in some applications, allow velocities to fall below the level needed to carry contaminants effectively.
The correct balance depends on the application. Grease-laden kitchen extract, dust extraction and general ventilation have different design requirements. This is why a one-size-fits-all duct diameter is not a dependable solution.
Calculate the likely pressure loss across the full system, including the canopy or collection point, filters, ESP units where fitted, duct length, bends, reducers, attenuators, weather louvres and discharge components. The selected fan must overcome this total resistance while still delivering the required airflow.
A fan chosen only by its headline airflow figure can disappoint once it is connected to real ductwork. Performance data must be considered at the operating pressure, not in isolation.
Plan Branches and Transitions Carefully
When one fan serves more than one extraction point, the branch layout needs particular attention. Air follows the path of least resistance. Without proper balancing, one branch may draw strongly while another receives inadequate extraction.
Arrange branches so that airflow distribution can be controlled and tested. Where appropriate, include balancing dampers and ensure they are accessible after installation. Avoid forcing two opposing air streams directly into each other at a junction, as this creates turbulence and wastes fan pressure.
Transitions should be gradual. A sudden change from a large rectangular section to a small round duct can create significant resistance and noise. Purpose-made transitions deliver a cleaner airflow path and provide a more professional, durable installation than improvised site alterations.
Build in Access for Cleaning and Inspection
An extraction system that cannot be accessed cannot be maintained properly. This is especially critical for commercial kitchen extract, where grease deposits can build up inside ductwork and increase fire risk. Access doors should be positioned to allow cleaning contractors to reach the full route, including changes of direction, vertical risers and areas downstream of filters or treatment equipment.
Do not treat access panels as an afterthought. If they are blocked by ceilings, boxed-in services or fixed equipment, they provide little practical value. Their size, spacing and placement should reflect the cleaning method and the duct geometry.
For industrial processes, access is equally valuable for checking dust accumulation, corrosion, damaged seals and general condition. Planning for inspection protects system performance and makes scheduled maintenance quicker and less disruptive.
Choose Materials That Match the Environment
Material choice should reflect what is travelling through the duct and the conditions around it. High-grade stainless steel is a dependable choice for many commercial kitchen extraction applications because it is durable, hygienic and suitable for demanding cleaning regimes. It also provides a premium finish where ductwork is visible.
Galvanised steel may suit less aggressive general ventilation applications, while specialist materials or coatings may be required where moisture, corrosive fumes or particular industrial contaminants are present. The ductwork must also be suitably sealed and jointed for the pressure and duty of the system.
For kitchen extract, fire performance, grease containment and cleanability should guide the specification. In the UK, installations must also be planned around relevant building, fire safety and environmental requirements. The exact standard and approval route can depend on the building type, local authority expectations and the specific use of the premises.
Consider Discharge Location Early
The discharge point affects more than the final section of ductwork. It can dictate the entire route. Extracted air needs to leave the building safely, without causing nuisance through odour, smoke, heat, noise or re-entrainment into doors, windows and fresh-air intakes.
Roof discharge is often effective because it provides elevation and separation, but it is not automatically the right answer. Structural loading, roof access, neighbouring properties, planning constraints and weather protection all need consideration. A wall discharge may be practical in some circumstances, provided the location and plume behaviour are properly assessed.
If odour or grease control is a concern, allow space for suitable filtration or treatment equipment. An ESP unit, for example, can form part of a wider kitchen extract strategy, but it must be matched to the airflow, installed correctly and maintained on schedule. Equipment cannot compensate for a badly designed duct route.
Do Not Forget Make-Up Air
Extraction removes air from a room. If replacement air is not provided, the space can become depressurised. Doors become difficult to open, cold draughts appear, combustion appliances may be affected and the extraction system may lose capture performance.
Make-up air should be planned alongside the extract route, not added after commissioning problems arise. The supply air needs to enter the space without blowing directly across the cooking plume or work process. In commercial kitchens, poorly positioned supply air can push heat and vapour away from the canopy rather than into it.
The right approach depends on the layout, building fabric, heating strategy and operating conditions. Tempered supply air may be justified where comfort and winter operation matter, while simpler arrangements may suit lower-duty spaces.
Coordinate Installation Before Fabrication
A detailed survey saves wasted material and delays. Confirm ceiling heights, wall build-ups, steelwork, plant locations, access routes and fixing points before fabrication begins. Large duct sections may fit on a drawing but be impossible to carry through an existing doorway, stairwell or service corridor.
Support design matters too. Ductwork must be securely fixed, adequately supported and arranged so its weight does not place strain on fans, canopies or treatment equipment. Allow for expansion, vibration isolation where needed and safe access for future works.
Custom fabrication is particularly valuable where standard sizes would create unnecessary offsets, poor transitions or awkward site modifications. A system designed around the actual building usually installs faster and performs more predictably than one forced from off-the-shelf sections.
Treat Commissioning as Part of the Design
The final test of a duct layout is measured performance, not how tidy it looks on installation day. Commission the system by checking airflow, fan duty, branch balance, capture performance and noise levels. Record the results and address restrictions before the site is handed over.
At CanopyMan, practical duct planning begins with the operating environment and ends with an extraction system that can be installed, cleaned and relied upon. A well-routed, correctly sized duct system protects the investment in every canopy, fan and filtration component connected to it.