Fume cupboards come in ducted or recirculating variants, but which is best for you?

As a general rule of thumb we would always recommend ducted (un-filtered) fume cupboards, as they offer a number of key advantages over recirculating (filtered) fume cupboards. However, budget, difficulty of installation and/or low usage can often favour a recirculating unit. Sometimes the best solution is a hybrid installation – a ducted fume cupboard with an external or in-line filtration system in the extract duct.
The main advantages and disadvantages of each are detailed below.

Consideration Ducted Fume Cupboard Recirculating Fume Cupboard
Purchase Price Generally higher than a recirculating model, but depends on the amount of duct required. Generally less than a ducted fume cupboard.
Installation Depending on the duct route and fan location installation can be disruptive. Planning permission may be required to install a sufficiency high discharge stack. Scaffolding and builders work (such as hole cutting through walls/roof etc.) may be required. Generally easy and quick to install, without the need for any builders work, planning permission etc.
Versatility and Use Extremely robust and versatile. Can be used with a very wide range of chemicals and processes. Frequency of use is not a concern. Limited to a very narrow range of chemicals. Frequency of use directly affects the life expectancy of the filters and needs to be closely monitored. Not recommended for use with very hazardous chemicals.
Running and Maintenance Costs Removes air from the lab, which needs to be replaced. This can be expensive if it needs to be cooled, heated or filtered. However, all labs need general ventilation. The fume cupboard extract system can compliment this or replace it entirely. Testing and maintenance costs are very low. Doesn’t need replacement air as cleaned air is returned directly to the lab. Filters needs regular and expensive saturation testing. Frequency of filter replacement depends on use but typically 1-3 years. Replacement filters are expensive (upwards of £800).
Safety Concerns Very few. Assuming the extract system is correctly installed to BS EN 14175 fume dispersal ensures that exposure limits are not exceeded and fumes do not enter breathable zones. Misuse, overuse or chemical spills can quickly saturate the filters and release fumes back into the lab. Poorly fitting, damaged or incorrectly specified filters will also allow fumes to return to the lab. Filter saturation alarms generally rely on hours of use and rarely monitor the quality of air exiting the fume cupboard. Not recommended for use with very hazardous chemicals.
Environmental Concerns Emit fumes into the atmosphere but rarely in volumes large enough to cause concern. Saturated carbon filters are classified as hazardous waste and need to be treated and disposed of accordingly.
Mobility Fixed in place. Expensive and disruptive to relocate. Generally freestanding and easy to relocate.

Contact us for further  information or advice on your fume cupboard requirements.

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