A welding extraction retrofit is rarely needed because a workshop has no ventilation at all. More often, there is an old fan, an undersized canopy, a poorly routed duct run, or a system that was installed before the current welding bays and production levels existed. The result is familiar: fume lingering around operatives, dust settling on equipment, extraction that sounds busy but does not capture at the point of generation, and a layout that has gradually outgrown its original design.
Retrofitting is a practical way to improve local fume control without rebuilding the entire workshop. The right scope depends on the welding process, the number of stations, where people stand, the available routes for ductwork and whether the existing equipment is worth retaining. A fan replacement alone can help in some cases, but it will not correct poor hood positioning or restrictive ductwork.
Start with the welding activity, not the fan
The fan is an essential part of an extraction system, but it should not be the first specification. Begin with what is being welded, where it is welded and how consistently each bay is used. MIG, TIG, MMA and cutting operations do not produce the same fume load or plume behaviour. The material being worked also matters, particularly where coatings, oils or stainless steel are involved.
Look at the job as it is actually carried out rather than how the workshop drawing says it should be carried out. Is welding performed on a fixed bench, on jigs, inside a fabrication cell, or on larger assemblies that move through the space? Does the operative need unrestricted access from several sides? Are two people working on one item? These details determine whether a fixed extraction canopy, a capture hood, flexible extraction arms or a purpose-made enclosure is the sensible route.
A canopy can be effective over a consistent work area where rising fume can be directed into the capture zone. It is less effective if the welder regularly works outside that zone, if cross-draughts disrupt the plume, or if large workpieces force the source of fume too far below the canopy. In those situations, a closer capture arrangement is normally more useful than simply fitting a larger fan.
Capture distance changes the whole design
The closer extraction is to the welding source, the less air needs to be moved through the system to achieve useful capture. This is why a well-positioned hood or arm can outperform a high-level canopy that is too far away. It also reduces the chance of drawing fume through the worker's breathing zone before it is extracted.
There is a balance to strike. A hood placed too close can obstruct access, interfere with fixtures or be damaged during handling. A practical retrofit provides enough adjustment for the operator to position capture close to the work without making every job awkward. If the system only works when everything is perfectly placed, it will not work consistently in a busy workshop.
Assess what the existing system can keep
Not every retrofit requires complete replacement. Sound ductwork may be retained if it is correctly sized, clean, reasonably airtight and routed without unnecessary resistance. Existing supports, roof penetrations and electrical supplies can also reduce installation disruption. However, retaining parts simply because they are already in place can create a poor-performing system around a new fan or canopy.
Inspect the full route from the capture point to discharge. Common problems include crushed flexible duct, long runs with multiple tight bends, undersized branches, makeshift connections and poor access for cleaning. Every restriction adds resistance. A fan selected without accounting for that resistance may deliver far less useful extraction at the hood than expected.
Ductwork should be treated as part of the extraction equipment, not an afterthought. Purpose-made spiral duct, elbows, spigots, reducers and fittings provide a cleaner, more predictable route than improvised sections. For industrial ductwork, DW144 provides the relevant standard framework for construction and installation quality. This is particularly valuable on larger or more complex retrofit work where air leakage, support spacing and access points affect long-term performance.
Where an old system has been in service for years, internal deposits deserve attention too. Build-up reduces free area and can make a previously adequate duct run restrictive. It may be more cost-effective to replace a difficult section than to design around its limitations.
Decide whether the fan is genuinely undersized
A fan can be the wrong choice for several reasons. It may not produce enough pressure for the duct route, it may have been selected for a previous layout, or it may be operating with a dirty filter or damaged impeller. The answer is not automatically a larger unit. Increasing fan duty against unsuitable ducting can increase noise, waste energy and still leave capture weak at the welding point.
A proper selection considers the required airflow at each capture point and the total resistance of the completed system. It should also account for whether several stations will run at once. If only one extraction arm is in use at a time, a different arrangement may be appropriate than a workshop where every bay is active throughout the shift.
For a retrofit, speed control can be useful where demand changes between jobs. It gives the operator or facilities team a means to match extraction output to use, but it is not a substitute for correct design. At maximum demand, the system still has to provide the required capture performance. CanopyMan supplies industrial extraction fans and is an authorised UK dealer for Soler & Palau fans and speed controllers, allowing the fan and control element to be specified as part of the wider system rather than as isolated components.
Filtration, discharge and make-up air
The route after the fan deserves the same attention as the capture point. Depending on the process and site constraints, extracted air may require filtration before discharge or a different arrangement for recirculation. Electrostatic precipitator units can form part of a filtration solution where appropriate, but suitability depends on the contaminant, maintenance regime and the overall system design.
Filtration is not fit-and-forget equipment. Any collection system needs planned inspection and cleaning. If maintenance access is poor, filters are likely to be neglected, pressure losses rise and the extraction performance gradually falls away. Build access into the retrofit from the start, including sensible locations for service doors, filter removal and safe isolation.
A workshop also needs replacement air. Removing air from a space without considering how fresh air enters can create unwanted draughts, make doors difficult to open or pull air from unsuitable areas. Make-up air should be introduced in a way that does not blow the welding plume away from the capture hood. This point is often missed when an old fan is replaced with a more capable unit.
Choose standard equipment where it fits, custom fabrication where it matters
Standard components are often the quickest and most economical route for straightforward welding bays. A standard canopy, fan and spiral duct arrangement can suit a fixed bench layout well, provided the capture position and duct route are correct. It also makes future replacements and extensions easier to plan.
Custom fabrication becomes worthwhile where the workshop has unusual roof heights, restricted wall space, non-standard bench dimensions or a requirement to work around cranes, racking or existing services. A made-to-measure canopy can be sized around the actual work area rather than forcing the process to fit an off-the-shelf dimension.
Material choice should be honest and proportionate. Standard stainless fabrication is commonly supplied in 430-grade stainless steel at 0.7 mm thickness. Where the environment, cleaning regime or specification calls for it, 304-grade stainless steel and alternative thicknesses can be made to order, at a higher price. The right choice depends on exposure, use and budget, not on paying for a grade that adds no practical benefit.
For canopy fabrication associated with commercial kitchen applications, DW172 is the relevant guidance. In workshop extraction, the key principle remains the same: the canopy must be manufactured and installed as part of a complete system, with its dimensions and connection details suited to the duty. A well-made canopy cannot compensate for poor capture geometry, and a good fan cannot compensate for a badly fabricated or poorly connected hood.
Plan installation around production
A retrofit should reduce disruption rather than create a second operational problem. Before ordering equipment, map the installation sequence: delivery access, lifting requirements, electrical work, roof or wall penetrations, duct supports and downtime for each welding bay. It may be possible to fabricate duct sections and canopies in advance, then complete the final changeover during quieter hours or a planned shutdown.
Commissioning matters as much as installation. Once fitted, check that hoods and arms are positioned for the tasks being done, that controls are understood, and that operators know when adjustments are needed. A system performs best when the people using it can see that it makes their working area clearer without slowing the job down.
The most worthwhile retrofit is not necessarily the biggest one. It is the one that captures fume where it is created, uses a duct route the fan can realistically serve, and remains practical for the workshop team to use and maintain shift after shift.