Five (Often Forgotten) Things To Consider Before Purchasing a Ducted Fume Cupboard

A ducted fume cupboard rarely arrives as a standalone purchase. It arrives attached to a venting route, a slice of the building fabric, and sometimes a planning application. None of the five things below are complicated on their own. What causes the trouble is timing. Each one tends to surface around Stage 4, when drawings are meant to be locked, and the fan position or duct run suddenly needs revisiting.

Here is where each of these five things actually belongs in your project timeline, and who should be holding it.

1. The venting route belongs in concept design, not fit-out

BS EN 14175 sets the standard here. The exhaust point from a ducted fume cupboard must vent vertically, extending to 1.25 times the overall building height or 3 metres above its highest point, whichever is greater. That is a roof level decision, which means it needs to sit with the architect and M&E consultant at Stage 1 to 2, alongside the initial building massing, not once the lab layout has already been drawn.

Leave it later than that, and you are retrofitting a stack position into a roof that was never designed around it.

2. Planning permission gets raised at Stage 2, not discovered at Stage 4

The height requirement above means an external stack can trigger a planning application, particularly for taller buildings or sites with restrictions on roof-mounted equipment. This is worth a conversation with your planning officer at concept design, run in parallel with the venting route decision, rather than something your contractor flags once the application is already submitted.

Routing the ductwork internally avoids planning in most cases but incurs its own coordination costs. You are looking at large holes through floors and walls, typically 250mm diameter for cupboards up to around 1800mm wide, rising to 315mm for anything larger. Either route needs deciding early enough that it shapes the drawings, not the other way round.

3. Price the ductwork, fan and installation into the cost plan at Stage 2 to 3

This is the cost that catches people out because it rarely appears on the fume cupboard quote. Running ductwork, sizing and supplying the fan, and connecting services can cost more than the cupboard itself, especially where the cabinet sits a long way from the fan and exhaust point.

Get a rough position for the cupboard agreed early enough that this cost can go into the Stage 2 to 3 cost plan alongside the rest of the mechanical package. Finding it at tender stage tends to mean finding it as a variation. Our guide to fume cupboard installation ductwork covers what a compliant run actually needs to include.

4. Fire collars need to be on the fire strategy, and the terminology matters

Fume extract ductwork is typically PVC or polypropylene, and where it passes through a fire-rated wall or partition, the correct product is a fire collar (also called an intumescent collar or sleeve), not a fire damper. A true fire damper is a mechanical device designed for rigid metal ductwork. Standard fire dampers are not compatible with plastic duct of this kind, so specifying one on a fume extract run is the wrong solution.

This needs coordinating with your fire strategy at Stage 3 to 4, when compartmentation is being finalised, and it is worth confirming directly with your installer that fire collars, not dampers, are what is being quoted. For a small installation, say ten cupboards, this can run to several thousand pounds, and it is a cost that belongs in the fire strategy discussion rather than turning up as a late addition.

5. Make-up air is a running cost decision, not just an installation one

Without a Variable Air Volume system, a single 1500mm cupboard can extract an average of 1076 cubic metres of air per hour, and that air needs heating or cooling depending on the season. You should expect energy bills to rise by at least £1,000 per cupboard per year on a constant volume system.

The CAV versus VAV decision affects both the capital cost and the running cost, and it is far easier to build into the ductwork and control system sizing at Stage 3 to 4 than to retrofit once the system is installed. If you are specifying multiple cupboards, this is worth modelling properly before the ductwork is sized rather than after.

Getting these five things into the right stage

None of this is about adding complexity to your project. It is about making sure venting, planning, ductwork cost, fire strategy and make-up air sit with the people making decisions at Stage 1 to 4, rather than landing on the fume cupboard supplier's desk once the building is largely designed. Our three simple steps to purchasing your first fume cupboard cover the wider process if you are starting from scratch, and our ducted fume cupboard range has the full technical specification once you are ready to start comparing units.

If you would like to talk through where any of these are positioned within your current programme, get in touch with our team.