A production line can be running to target while the air around it quietly creates the next operational problem. Welding fume, oil mist, dust, heat and vapours do not stay where they are produced. They spread through work areas, settle on equipment and put pressure on people, maintenance schedules and compliance. This factory ventilation planning guide sets out how to plan a system around the real source of contamination, rather than simply fitting fans and hoping for the best.
Start with the process, not the fan
The right ventilation system begins with a clear view of what happens on the factory floor. A general extraction rate might improve the feel of a space, but it will rarely control a contaminant effectively when it is released at a machine, bench or process vessel. The first priority is to identify where contaminants are generated, how they move and who is exposed.
Walk the site while it is operating normally. Observe the position of operators, the working height of machinery, doors that are opened regularly and any existing air movement. A welding bay, for example, may need close-capture extraction at the workpiece. A hot process may require a purpose-built extraction canopy above the source, balanced with enough replacement air to prevent poor capture. A dusty cutting process may need enclosed extraction points rather than an overhead solution.
A proper survey should record five practical details:
- the contaminant or heat source, including when it is produced
- the number of extraction points required and their likely position
- the size, layout and construction of the building
- existing duct routes, roof penetrations and access restrictions
- nearby processes that could be affected by noise, draughts or negative pressure
Assess the contaminant and exposure risk
Not all airborne contaminants behave in the same way. Fine welding fume can remain suspended and travel a considerable distance. Grinding dust may fall quickly but become airborne again when disturbed. Oil mist from machining can coat surfaces, reduce visibility and load filters rapidly. Solvent vapours, depending on their properties, may create wider safety considerations and require carefully selected equipment.
The level of control required depends on the process, the duration of exposure and the people working nearby. In many cases, local exhaust ventilation is the most efficient route because it removes contamination close to its release point. General ventilation still has a role, particularly for background heat, humidity and low-level airborne contamination, but it should not be treated as a substitute for source capture where a process produces harmful fume, dust or mist.
In the UK, the system design should support the employer’s wider duties under workplace health and safety requirements. That means considering exposure limits, suitable control measures, inspection requirements and documented testing. A ventilation supplier can help develop the equipment specification, but the factory operator should also ensure the wider risk assessment reflects the planned installation and the process it will serve.
Size extraction for capture, not headline airflow
High airflow figures can look reassuring on a quotation. They are not enough on their own. The useful question is whether the extraction point captures the contaminant before it reaches the operator’s breathing zone.
Capture depends on airflow volume, air velocity at the source, hood shape, the distance between the hood and the process, and the effect of surrounding draughts. Moving an extraction hood a short distance away from a welding position can dramatically reduce its effectiveness. Likewise, a large open-fronted booth may need substantially more airflow than a well-designed enclosure handling the same process.
This is why custom fabrication matters. A standard stainless steel canopy or industrial hood may suit a straightforward operation, while a bespoke design may be the better long-term choice for unusual machinery, restricted headroom or a changing production layout. The aim is not to make the hood bigger than necessary. It is to make its geometry work with the process so that the fan capacity, duct size and energy use are all proportionate.
A good designer will also calculate pressure losses across the full system. Duct length, bends, branches, dampers, filters, weather louvres and discharge arrangements all add resistance. If the fan is selected only from a required airflow figure, without allowing for system resistance, performance at the extraction point can fall short once installed.
Plan make-up air from the beginning
Every litre of extracted air has to be replaced. If it is not, the building can become depressurised. Doors become harder to open, cold air enters through gaps, extraction performance becomes unpredictable and heaters work harder. In some factories, negative pressure can also draw in contaminants from adjoining areas.
Make-up air should be planned alongside extraction, not added as an afterthought. It may be introduced through dedicated supply units, filtered wall louvres or carefully positioned air inlets, depending on the building and process. During colder months, heated make-up air can be justified where large volumes are extracted continuously. The capital cost is higher, but the reduction in heating demand and improved operator comfort can make the case strong for high-use facilities.
Placement matters as much as volume. Supply air directed across an extraction point can push fume away from the hood. Air should support the path towards extraction without creating uncomfortable draughts at workstations.
Design ductwork for performance and service access
Ductwork is not simply a route from hood to fan. Its diameter, material, bends and branch design determine how much energy the fan needs and whether dust, grease or mist can accumulate inside the system.
Keep routes as short and direct as the building allows. Avoid unnecessary sharp bends, undersized ductwork and improvised connections. Where particulate is present, duct velocity must be suitable for carrying material through the system rather than allowing it to settle. Where corrosion, heat or grease are factors, material selection becomes equally important.
Stainless steel ductwork, hoods and fabricated components provide a durable option for demanding applications, particularly where hygiene, moisture resistance or regular cleaning are priorities. Access doors should be incorporated where cleaning and inspection will be needed. A system that cannot be serviced efficiently will lose performance and become more expensive over its working life.
Discharge location also deserves attention. Extracted air should not be released where it can re-enter through doors, windows or air intakes, affect neighbouring premises or create nuisance at ground level. This is a design issue, not a final installation detail.
Choose filtration and controls to suit operating hours
Filtration protects the fan, controls emissions and can allow cleaner air handling, but it creates resistance. The finer the filtration requirement, the more carefully the system needs to be sized and maintained. For oil mist, welding fume and certain fine particulate applications, multi-stage filtration or electrostatic precipitator units may be appropriate. The right arrangement depends on the contaminant, airflow volume, discharge requirements and maintenance capability on site.
Do not select filters solely on their purchase price. Consider pressure drop, replacement intervals, cleaning procedures, disposal costs and whether the system has indicators to show when performance is declining. A blocked filter can turn a well-designed installation into an underperforming one.
Controls should reflect how the factory actually works. Variable-speed drives can reduce fan energy use where machinery runs intermittently or production shifts vary. Interlocks can ensure extraction operates when the associated process starts. Simple visual indicators and pressure gauges give supervisors an immediate sign that airflow needs attention. For a site with fixed, continuous production, a simpler constant-volume system may be the most reliable choice.
Build commissioning and maintenance into the budget
Installation is not the end of the project. Commissioning proves whether air is moving where the design intended and whether the extraction points deliver the required performance. Airflow measurements, fan settings, system balancing and operator checks should be recorded before handover.
Operators also need a clear routine. Hoods must be positioned correctly, movable arms should be placed close to the work, and access doors must be kept closed during operation where required. Even premium-quality equipment cannot perform properly when the capture point is moved out of position or filters are left beyond their service interval.
Planned maintenance should cover fan condition, belts or drives where fitted, filter loading, duct cleanliness, hood damage and controls. Statutory thorough examination and testing requirements for local exhaust ventilation should be built into the site’s compliance calendar. Treat this as a production-protection task, not paperwork. It helps prevent downtime, protects equipment and gives staff confidence that the workplace is being properly managed.
Turn the plan into a workable installation
The strongest factory ventilation plans balance capture performance, energy use, access, budget and future expansion. A system designed only for today’s machinery can become restrictive when a new line is added or a process changes. Allowing for spare fan capacity, accessible branch connections or modular filtration can be worthwhile where growth is likely, although oversizing every component without evidence only wastes capital and energy.
CanopyMan can manufacture and install fully customised stainless steel extraction solutions around the dimensions, process and routing constraints of an operating site. The practical value lies in getting the hood, ductwork, fan and filtration elements designed as one system rather than as separate purchases.
Plan around the contaminant, verify the airflow at commissioning and maintain the system with the same discipline applied to production machinery. That is how ventilation becomes a dependable part of a safer, more productive factory.