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Fume Cupboards Explained: Ducted vs Ductless, and How to Choose the Right One

  • Aug 19
  • 8 min read

Key takeaways

A fume cupboard protects you from chemicals. A biosafety cabinet protects you from biological agents. A laminar flow cabinet protects neither. Choosing on price rather than hazard is the most expensive mistake in this category, because the wrong enclosure offers no protection at all against the hazard you actually have.

The real decision is ducted or ductless, and it is decided by your chemistry, not your budget. Ducted cupboards handle anything. Ductless recirculating cabinets handle a defined list of compounds at defined loadings, cost far less to install, and need no building work.

Installed cost is where budgets break. The cabinet is often the smaller half of a ducted project once ducting, fan, roof penetration, make-up air and commissioning are counted. A ductless cabinet at £3,944.85 arrives on a bench and works.


What is a fume cupboard?

A fume cupboard is a ventilated enclosure that draws air away from the operator across a work surface, capturing hazardous vapours, gases, dusts and aerosols and either discharging them outside the building or filtering them before returning the air to the room.

The working principle is simple. Air enters through the open front beneath a movable sash, passes over the work, and is drawn out at the back. The inward velocity at the face is what keeps contaminated air away from your breathing zone. Everything else in the design exists to keep that velocity stable and predictable.

You will see them called fume cupboards, fume hoods, fume cabinets and extraction cabinets. In UK usage "fume cupboard" is the standard term and is the wording used in British and European standards. In North America the same equipment is a fume hood.


Fume cupboard, biosafety cabinet or laminar flow cabinet?

Match the enclosure to the hazard. Chemical vapour needs a fume cupboard. Infectious material needs a biosafety cabinet. Sterile work with no hazard to the operator needs a laminar flow cabinet.


Fume cupboard

Biosafety cabinet

Laminar flow cabinet

Protects operator

✔ from chemicals

✔ from biological agents

✘

Protects sample

✘

✔

✔

Air over the work

Room air, unfiltered

HEPA filtered

HEPA filtered

Exhaust

Ducted out, or carbon filtered

HEPA filtered

Back to room

Right for

Solvents, acids, powders, digestion

Cell culture, clinical microbiology

Media pouring, sterile assembly, electronics

Wrong for

Anything infectious

Volatile toxic chemicals

Any hazard to the operator

The dangerous confusion runs in one direction. A laminar flow cabinet blows filtered air outward, straight past the operator. Using one for solvent work aims the hazard at your face. If you are choosing between the sterile options, our laminar flow cabinets guide covers horizontal against vertical, and the biosafety cabinets guide covers Class I, II and III.

Ducted or ductless: which do I need?

Ducted if your chemistry is varied, unpredictable, high volume or includes anything a carbon filter cannot hold. Ductless if you use a defined set of compounds at modest quantities and need a working solution without building work.


Ducted fume cupboard

Ductless fume cabinet

Where the air goes

Discharged outside

Filtered, returned to the room

Chemical range

Effectively unlimited

Defined by filter type and loading

Perchloric acid, hydrofluoric acid, high-volume solvent

Suitable with correct specification

Not suitable

Building work

Ducting, fan, roof or wall penetration

None

Make-up air

Must be designed in

Not required

Mobility

Fixed

Portable

Consumables

Minimal

Carbon filters, pre-filters

Heating cost

Conditioned air lost continuously

None

Typical lead time

Weeks, plus contractor scheduling

Days

The point people miss is that a ducted cupboard is a building project, not a purchase. You are committing to a duct route, a fan, a discharge point at a safe height, make-up air so the room does not go into negative pressure, and often planning consent. Once a laboratory is built and occupied, that work is disruptive and expensive, and in leased premises it may not be permitted at all.

That is precisely the gap ductless cabinets fill. They are not a compromised fume cupboard. They are a different tool that solves a narrower problem completely.


How does a ductless fume cabinet actually work?

Air is drawn through the open front, across the work surface, and up through a filter stack. A pre-filter catches particulates and protects the expensive filter behind it. The main carbon filter adsorbs organic vapours. Cleaned air returns to the room.

Three things determine whether this is safe for your work.

Filter chemistry must match your compounds. Standard activated carbon handles a broad range of organic solvents. Impregnated carbons handle specific groups such as acids, ammonia, formaldehyde or mercury. A general-purpose filter is not a universal filter.

Loading must be within capacity. Carbon adsorbs a finite mass. Occasional milligram-scale work is very different from decanting litres daily. Quantity, not just identity, decides suitability.

Breakthrough must be managed. Carbon does not fail loudly. It saturates, and then vapour passes through. This is why filter monitoring, a service schedule and a documented change interval are not optional extras. Treat filter replacement as a running cost from day one.

If you cannot state your compounds and your quantities, you cannot specify a ductless cabinet, and the honest answer is a ducted cupboard.


The ductless fume cabinet we stock

Chemcap Clearview Ductless Fume Cabinet, £3,944.85 including 15% off, reduced from £4,641.00. SKU BC1004+FB0005/04+FP0004. One unit in stock at the time of writing.

Supplied complete with pre-filter, MP type carbon filter and LED lighting. External dimensions 1000 × 570 × 1145 mm (W × D × H), so it fits a standard bench run without modification.

The specification points that matter:

Average face velocity of 0.5 m/s. This sits at the upper end of the range usually specified for containment enclosures and is the number to quote when someone asks whether the cabinet is doing anything.

Audible low airflow alarm. Without an alarm you have no way of knowing that a loaded filter has raised resistance and dropped your face velocity. This is the feature that separates a containment device from a box with a fan in it.

Safe-change pre-filter, baggable under negative pressure. The filter change is the one moment when everything the cabinet has captured is in your hands. Bag-in bag-out handling means it stays contained.

Service due indicator. A prompt against the maintenance schedule, which under COSHH you have to be able to evidence.

Quiet operation, below 50 dB(A), and lockable front access doors. Noise decides whether people actually use the cabinet. Locks decide who can open the filter housing.

Fully portable. No ducting, no penetrations, no contractor. It can be moved when the lab is reconfigured, which for a leased building is often the deciding argument.

The unit is a recirculatory carbon filtration cabinet, sometimes described as a ductless fume hood. It suits containment of chemical fume hazards where the compounds are known, and it is a common way to add ventilated bench space when a laboratory has run out of fume cupboard capacity and cannot easily install more.


What if I need a ducted cupboard?

We do not hold ducted fume cupboards as stock items, so if your work needs one, talk to us rather than ordering from this page. Specification depends on your duct route, discharge point and make-up air strategy, and none of that can be chosen from a product listing.

Bring the following to that conversation and it will be a short one: the compounds and quantities you work with, the internal width you need, the position of the nearest external wall or roof void, whether the room has mechanical supply air, and whether the building is owned or leased.

For work in and around a cupboard, we do stock supporting equipment. The LabJaws stainless steel lab frame kits are sized to fit inside fume enclosures and give you a rigid support structure for glassware and apparatus:

For Kjeldahl digestion, where acid fume extraction is part of the method rather than a room-level problem, the Velp JP recirculating water pump for fumes aspiration at £1,600.75 handles aspiration on DK series digesters directly.

You can see the full containment range on the Cabinets category page.


What does COSHH require once the cupboard is installed?

Buying the equipment is the start of the obligation, not the end of it.

Use it correctly. Work at least 150 mm inside the front plane, keep the sash at or below the marked working height, and do not use the cupboard as a storage cupboard. Bottles clustered at the back disrupt the airflow pattern the design depends on.

Do not defeat the airflow. Large equipment on the work surface creates turbulence and dead zones. Raise bulky items on blocks so air can pass beneath them.

Test and examine it. Local exhaust ventilation must undergo a thorough examination and test at least every 14 months, and the record must be kept. In practice most laboratories run an annual cycle so the date never drifts past the limit. HSE guidance note HSG258, "Controlling airborne contaminants at work", is the reference document for how LEV should be specified, commissioned and tested.

Train the people using it. COSHH requires that anyone exposed to substances hazardous to health receives instruction and training. For a fume cupboard that means face velocity, sash discipline, alarm response and what to do about a spill.

Check DSEAR separately if you handle flammables. The Dangerous Substances and Explosive Atmospheres Regulations apply to flammable solvent work independently of COSHH, and they influence electrical specification inside and around the enclosure.


How much does a fume cupboard cost in the UK?

Two different answers, which is exactly why the question is hard to research.

A ductless cabinet is a single price. Our Chemcap Clearview unit is £3,944.85, delivered and working, plus filters as a running cost.

A ducted cupboard is a project cost. The cupboard itself is one line. Ducting, extract fan, roof or wall penetration and weathering, make-up air provision, electrical work, commissioning and airflow testing are the others, and on a retrofit into an occupied building they frequently exceed the cost of the cupboard. Budget the project, not the product, and get the duct route surveyed before you commit to a model.

Filters are the ongoing cost on the ductless side. Replacement interval depends on your compounds and loading, so build it into the running budget rather than treating it as an unpleasant surprise in year two.


Frequently asked questions

Can I use a fume cupboard for microbiological work? No. A fume cupboard protects you from chemical vapour but does nothing to protect the sample, and it is not designed or tested for containment of infectious aerosols. Biological work needs a cabinet tested to BS EN 12469. See the biosafety cabinets guide.

Is a ductless fume cabinet as safe as a ducted fume cupboard? For the compounds and quantities it is specified for, yes. Outside that specification, no. The safety of a ductless unit depends entirely on the filter matching your chemistry and on the filter being changed before breakthrough. A ducted cupboard removes the contaminant from the building regardless of what it is.

How often do carbon filters need replacing? It depends on which compounds you use and how much. There is no universal interval. Establish one for your actual work, monitor it, and treat the service due indicator and airflow alarm as prompts rather than guarantees.

What face velocity should a fume cupboard have? Containment enclosures are typically specified in the region of 0.3-0.5 m/s at the working sash height. Our ductless cabinet runs at an average of 0.5 m/s. The number matters less than whether it is stable, measured and recorded.

Do I need planning permission to install a fume cupboard? Potentially, if the installation involves an external discharge stack. This is one of the practical reasons laboratories choose ductless units for retrofit work, along with the disruption of running ducting through an occupied building.

Can a fume cupboard be moved later? A ducted cupboard, not without redoing the ductwork. A ductless cabinet, yes. Ours is fully portable, which matters if you are in leased premises or expect to reconfigure the lab.


Sources and standards referenced

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