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Kitchen extraction cleaning - filtration stages
Some extraction systems have more than grease filters - a pollution-control or odour-control unit with further filtration stages: cartridge, bag, carbon or HEPA filters. These are easily forgotten, out of sight in the plant - but they clog, and they need cleaning or replacing. Here are the filters you forget, and why they matter. This is general commentary.
The short answer
Most people think of extraction filtration as the grease filters in the canopy - but some systems have additional filtration stages beyond the grease filters and ductwork, and these are the filters that get forgotten. Where these extra stages are found: systems with a pollution-control unit or odour-control unit - often fitted where the extracted air must be cleaned before discharge (for example where the discharge is near residents or other premises, where planning conditions require reduced grease, smoke or odour, or in sensitive locations). These units contain further filtration stages to clean the air. The stages that may be present: cartridge or bag filters (further grease and particulate filtration); electrostatic precipitators (ESPs - which use a charge to remove fine particles and grease, and have collector cells that need cleaning); carbon filters (activated carbon, to remove odour); and HEPA or fine-particulate filters (to remove very fine particles). So a system with pollution/odour control has these secondary stages, each doing further cleaning of the air. Why they are forgotten: they are out of sight, in the plant/unit (often on the roof or in a plant room), not part of the visible kitchen - so they are easy to overlook, especially if the focus is on the visible canopy and grease filters. Why they matter: these stages load up and clog over time (with grease, particulate, or exhausted carbon), and when they do, they lose effectiveness (so the discharge is no longer cleaned - worse grease, smoke or odour emitted, which can breach planning conditions or upset neighbours) and can restrict the airflow (reducing extraction). So they need their own cleaning or replacement regime: cartridge and bag filters cleaned or replaced, ESP cells cleaned, carbon filters replaced when exhausted, HEPA filters replaced when loaded - at intervals matched to their loading. So if your system has these stages, they must be included in the maintenance - not forgotten. The filters you forget still clog and still need attention. So cartridge and HEPA stages, and other secondary filtration, are the easily-forgotten filters that still need cleaning or replacing. This is general commentary on extraction filtration.
Key points
Beyond the grease filters
The starting point is that some extraction systems have more filtration than just the grease filters in the canopy - additional stages that clean the air further, which many people do not realise are there. A basic extraction system has grease filters (in the canopy), ductwork, and a fan, discharging the air outside. But some systems have more: a pollution-control unit or odour-control unit fitted into the system (usually before the discharge point), containing further filtration stages to clean the extracted air before it is released.
These extra stages are fitted where the discharge needs to be cleaned - which is often required in certain situations: where the extraction discharges near residents or other premises (so grease, smoke and odour in the discharge would cause a nuisance); where planning conditions require the discharge to be cleaned (reduced grease, smoke or odour - common for new or changed premises in sensitive locations); or in other situations where the raw extract discharge would be unacceptable. So a system with pollution or odour control has these additional filtration stages doing further cleaning - beyond the grease filters. If your system has such a unit, it contains filters that are part of the system but easily overlooked. Understanding that these extra stages exist (in systems that have them) is the first step to not forgetting them. So beyond the grease filters, some systems have extra filtration stages. So systems with extra filtration go beyond the grease filters. This is general commentary.
The stages
The additional filtration stages in a pollution/odour-control unit can include several types - cartridge and bag filters, electrostatic precipitators, carbon filters, and HEPA/fine filters - each doing a further stage of cleaning. Cartridge and bag filters: further grease and particulate filtration beyond the canopy grease filters - cartridges or bags that catch finer grease and particles, loading up over time. Electrostatic precipitators (ESPs): units that use an electrical charge to remove fine particles and grease from the air (charging the particles and collecting them on plates/cells) - highly effective for fine grease and smoke, but the collector cells load up with the collected grease and need regular cleaning to keep working.
Carbon filters: activated carbon filters that adsorb odours from the air (removing cooking smells before discharge) - the carbon becomes exhausted (saturated) over time and needs replacing to keep removing odour. HEPA or fine-particulate filters: very fine filters that remove very fine particles - used where a high standard of particulate removal is needed; they load up and are replaced when full. So the stages a system might have include cartridge/bag filters (grease/particulate), ESPs (fine grease and smoke), carbon (odour), and HEPA (fine particulate) - in various combinations depending on what the discharge needs to remove (grease, smoke, odour, fine particles). Each is a filtration stage that does its job until it loads up or is exhausted, then needs cleaning or replacing. So the stages are cartridge, ESP, carbon and HEPA - each a further cleaning step with its own maintenance. So cartridge, ESP, carbon and HEPA are the possible stages. This is general commentary.
Why they are forgotten
These secondary filtration stages are easily forgotten - and the reason is that they are out of sight, in the plant, not part of the visible kitchen. The pollution/odour-control unit and its filters are usually located away from the kitchen - on the roof, in a plant room, or in the ductwork run before discharge - so they are not visible or present in the day-to-day kitchen. Out of sight, they are out of mind: the kitchen's attention is on the visible canopy and grease filters (which are in the kitchen, obviously loading up with grease), while the hidden secondary stages are easy to overlook.
It is also easy to forget they exist at all: a kitchen may not fully realise its system has a pollution-control unit with additional filters (especially if it was installed by others, or the operator inherited the premises), or may not know what maintenance those filters need. And because the grease filters and even the ductwork are more obviously 'the extraction', the secondary stages can fall outside the cleaning that is arranged (a grease clean that does the canopy, filters and ductwork may not include the pollution-control unit's filters unless specified). So the secondary stages are forgotten because they are out of sight in the plant, easy to overlook, and outside the usual focus - even though they are part of the system and need maintenance. This is why they are 'the filters you forget'. So they are forgotten because they are out of sight in the plant. So out of sight in the plant is why they are forgotten. This is general commentary.
Why they matter
The reason it matters not to forget these stages is that they load up and clog over time - and when they do, they stop cleaning the discharge and can restrict the airflow. Loss of effectiveness: each stage does its job (removing grease, particulate, or odour) until it loads up or is exhausted - a loaded cartridge or bag, a dirty ESP cell, an exhausted carbon filter, a full HEPA filter. Once loaded/exhausted, the stage no longer cleans the air effectively - so the discharge is no longer cleaned to the standard it should be: more grease, smoke or odour is emitted. This matters because the whole point of the unit was to clean the discharge (for the neighbours, the planning conditions, the environment) - so a neglected stage means a discharge that breaches the requirement or causes a nuisance (upset neighbours, odour complaints, a planning breach).
Restricted airflow: a clogged filter stage also restricts the airflow through the system (like a clogged grease filter), reducing the extraction - so the kitchen's extraction performance suffers (a hotter, worse-ventilated kitchen) if the secondary stages are clogged. And in the case of an ESP, a dirty cell can arc or fail. So neglecting the secondary stages has real consequences: a discharge that is no longer cleaned (nuisance, planning breach), and reduced extraction (worse kitchen conditions). This is why they matter and must not be forgotten - they are doing an important job (cleaning the discharge, and passing the airflow), and they only do it while maintained. So they matter because they clog and lose effectiveness, harming the discharge and the airflow. So they clog and lose effectiveness - which is why they matter. This is general commentary.
Don't forget them
So if your extraction system has secondary filtration stages - a pollution-control or odour-control unit with cartridge, bag, ESP, carbon or HEPA filters - they must be included in the maintenance, not forgotten: they load up and clog like any filter, losing effectiveness (worse discharge) and restricting airflow, so they need their own cleaning or replacement regime, at intervals matched to their loading. So don't forget the secondary stages - include them in the maintenance.
This connects to a complete approach to extraction maintenance - one that covers the whole system, including the parts that are out of sight. A proper extraction maintenance regime should account for all the filtration and components the system actually has: the grease filters and canopy, the ductwork, the fan, and - where fitted - the secondary filtration stages (cartridge, ESP, carbon, HEPA). Each needs its appropriate cleaning or replacement at its interval: the grease filters and system cleaned to TR19 Grease, and the secondary stages cleaned or replaced per their type and loading (ESP cells cleaned, cartridge/bag filters cleaned or replaced, carbon and HEPA filters replaced when exhausted/full). So when arranging extraction maintenance, make sure the whole system is covered, including any pollution/odour-control unit's filters - which are easy to forget but still need attention. A competent extraction maintenance provider will identify and include these stages. So don't forget the filters you forget - include the secondary filtration stages in a complete maintenance regime. This is general commentary on extraction filtration.
Questions
They are additional filtration stages, beyond the canopy grease filters, found in systems with a pollution-control or odour-control unit that cleans the extracted air before discharge. A basic system has grease filters, ductwork and a fan; but some systems have more - a pollution/odour-control unit containing further filtration stages to clean the air (fitted where the discharge must be cleaned, for example near residents or where planning requires it). These stages can include cartridge or bag filters (further grease and particulate filtration), electrostatic precipitators (ESPs - removing fine particles and grease electrically), carbon filters (activated carbon, removing odour), and HEPA or fine-particulate filters (removing very fine particles) - in various combinations depending on what the discharge needs to remove (grease, smoke, odour, fine particles). So cartridge and HEPA stages (and ESPs, carbon, bag filters) are secondary filtration stages that clean the air further before discharge. They are part of the system but often overlooked, being out of sight in the plant. So they are the additional filtration stages in systems with pollution/odour control. This is general commentary.
Because they are out of sight, in the plant, not part of the visible kitchen - so they are easy to overlook. The pollution/odour-control unit and its filters are usually located away from the kitchen (on the roof, in a plant room, or in the ductwork before discharge), so they are not visible or present in the day-to-day kitchen. Out of sight, they are out of mind: the kitchen's attention is on the visible canopy and grease filters (obviously loading up with grease in the kitchen), while the hidden secondary stages are easy to overlook. It is also easy to forget they exist at all - a kitchen may not realise its system has a pollution-control unit with additional filters (especially if installed by others or inherited), or know what maintenance they need. And because the grease filters and ductwork are more obviously 'the extraction', the secondary stages can fall outside the cleaning that is arranged unless specified. So they are forgotten because they are out of sight in the plant, easy to overlook, and outside the usual focus - even though they are part of the system and need maintenance. So they are easily forgotten because they are hidden in the plant. This is general commentary.
They clog and lose effectiveness - so the discharge is no longer cleaned (worse grease, smoke or odour emitted), and the airflow can be restricted (reducing extraction). Each stage does its job until it loads up or is exhausted (a loaded cartridge or bag, a dirty ESP cell, an exhausted carbon filter, a full HEPA filter) - and once loaded, it no longer cleans the air effectively, so the discharge is no longer cleaned to the standard it should be. This matters because the unit's purpose was to clean the discharge (for the neighbours, planning conditions, the environment) - so a neglected stage means a discharge that breaches the requirement or causes a nuisance (odour complaints, a planning breach, upset neighbours). A clogged stage also restricts the airflow through the system (like a clogged grease filter), reducing the extraction - so the kitchen's extraction suffers (hotter, worse-ventilated) if the secondary stages are clogged. And a dirty ESP cell can arc or fail. So neglecting the secondary stages harms the discharge (nuisance, planning breach) and the airflow (worse extraction) - which is why they must be maintained. So neglect makes them clog, harming the discharge and airflow. This is general commentary.
Each has its own cleaning or replacement regime, matched to its loading: cartridge and bag filters cleaned or replaced; ESP cells cleaned; carbon filters replaced when exhausted; HEPA filters replaced when loaded. Cartridge and bag filters load up with grease and particulate and are cleaned (if cleanable) or replaced (if not) when loaded. Electrostatic precipitator (ESP) cells collect grease and particles and need regular cleaning (washing the cells) to keep working - a key maintenance item, as a dirty ESP loses effectiveness and can fail. Carbon (odour) filters have activated carbon that becomes exhausted (saturated) over time and is replaced when it stops removing odour (carbon is generally replaced, not cleaned). HEPA/fine filters load up with fine particulate and are replaced when full (not cleaned). So the maintenance is a mix of cleaning (ESP cells, some cartridges) and replacement (carbon, HEPA, some cartridges/bags), each at intervals matched to how quickly it loads/exhausts (which depends on the cooking and use). So these stages are maintained by cleaning or replacing them per their type and loading - which needs to be built into the extraction maintenance regime. So each is cleaned or replaced per its type and loading. This is general commentary; the specifics depend on your unit.
Not necessarily - a grease clean (TR19 Grease) focuses on the grease filters, canopy, ductwork and fan, and may not include the pollution/odour-control unit's secondary filters unless specified. The standard extraction grease clean addresses the grease-bearing parts of the system (filters, canopy, ductwork, fan) to control the fire risk - and the secondary filtration stages in a pollution/odour-control unit (cartridge, ESP, carbon, HEPA) are a different thing (cleaning the discharge, not primarily the fire risk), often out of sight in the plant, so they may fall outside a standard grease clean unless it is specified to include them. So it is important, if your system has these stages, to ensure they are included in the maintenance - either as part of the extraction cleaning (specified to cover the whole system including the pollution-control unit) or as a separate maintenance task. A competent provider will identify whether your system has secondary stages and include or advise on them. So do not assume a normal grease clean covers the secondary stages - check, and ensure they are included, because they need their own maintenance. So a normal clean may not include them unless specified. This is general commentary.
Check whether your system has a pollution-control or odour-control unit - if it does, it has secondary filtration stages that need maintaining. Systems with these extra stages have a unit (often on the roof or in a plant area) between the ductwork and the discharge, containing the additional filters (cartridge, ESP, carbon, HEPA). Signs you may have one: your premises is in a location where the discharge had to be cleaned (near residents, a sensitive location); planning conditions for your premises required grease, smoke or odour reduction in the discharge; or the system was designed with air/odour cleaning. If you are unsure, a competent extraction cleaner or engineer can inspect your system and identify whether it has a pollution/odour-control unit and what filtration stages it contains - and then advise on the maintenance those stages need. It is worth checking, because if you have these stages and are not maintaining them, they may be clogged and failing (harming your discharge and airflow) without your realising. So find out whether you have a pollution/odour-control unit - and if so, ensure its stages are maintained. So check for a pollution/odour-control unit to know if you have these stages. This is general commentary.
If your system has a pollution or odour-control unit, its cartridge, ESP, carbon or HEPA filters clog and need attention - but are easy to forget. Our extraction cleaning covers the whole system, identifying and including the secondary filtration stages. Ask us to check and maintain your full system, not just the grease filters.
