Phoenix Journal · Extraction
The grease filter is the first thing your extract system does to protect the ductwork behind it - and the cheapest decision to get right before anything is installed. Specify it properly at design stage and you buy yourself years of easier cleaning, lower fire risk and fewer arguments with your insurer.
Almost every problem we are called out to fix in a commercial kitchen extract system can be traced back to a decision made, or not made, at design stage.
The grease filter sits at the front line of that system. It is the barrier between the flame and the miles of ductwork, fan and roof plant behind it, and it is the single component that decides how much grease gets past the canopy and into places that are expensive and disruptive to clean. Get the filter right on the drawings and everything downstream becomes easier - the ductwork stays cleaner for longer, access is designed in rather than retrofitted, and the whole system stands a much better chance of passing muster with an insurer or environmental health officer.
Get it wrong and you inherit a system that sheds grease into the duct from day one. That is the version we meet most often: a canopy full of the cheapest filters that would fit, running at the wrong face velocity, draining onto a surface that was never meant to collect grease. This article walks through what to pin down before anything is ordered, and the current UK standards that should be shaping those choices.
The standards that should be on the table
There is no single Act that tells you which grease filter to buy, but there is a well established framework that everyone downstream expects you to have followed. The starting point is DW172, the BESA Specification for Kitchen Ventilation Systems (2nd edition, 2018). It is not statute, but it is the recognised industry benchmark for canopy and extract design in the UK, and it is what environmental health officers, insurers and consultants reach for when they want to assess whether a system was designed properly. DW172 covers canopy geometry, grease filtration, air volumes and discharge, so filter selection cannot really be separated from the canopy it sits in.
Alongside it sits the BS EN 16282 series, the European standard for equipment in commercial kitchens. Part 1 sets out the general requirements and the airflow calculation methods, while BS EN 16282-6:2020 deals specifically with aerosol separators - the formal name for grease filters - and their design and safety requirements, including how their efficiency is tested and classified. If a manufacturer quotes you a capture efficiency, this is the family of test methods it should trace back to, so ask for it in writing rather than accepting a headline percentage.
The third document is TR19 Grease, published by BESA in 2019 as the specification for fire risk management of grease accumulation in extraction systems. It governs how the system is cleaned and inspected once it is live, but it belongs in a design conversation because it sets the yardsticks you will be measured against for the life of the building - a mean grease deposit below 200µm across the system, and immediate localised cleaning where any single reading exceeds 500µm. A filter choice that lets grease stream past those thresholds is a design decision you will pay for every quarter.
Mesh or baffle, and the face velocity that decides it
The first real choice is filter type, and for most commercial extraction the answer is a stainless steel baffle filter rather than a mesh panel. Mesh filters are cheap and they do trap grease, but they hold it inside the media instead of shedding it, they clog quickly, they are awkward to clean thoroughly and a grease saturated mesh sitting directly above a flame is exactly the fire load you are trying to design out. Baffle filters force the air to change direction several times, flinging grease droplets onto the vanes where they run down and drain away, and they are built to be pulled out and put through a dishwasher or soak tank without falling apart. That draining behaviour is the whole point, which is why the way a filter sheds grease matters as much as the way it captures it.
What people miss is that a baffle filter only earns its capture figure - commonly quoted at around 90% - when it is running at the face velocity it was designed for. This is where filter selection and canopy sizing collide. Too few filters, or filters that are physically too large for the air volume, and the velocity across each one drops, the air no longer changes direction sharply enough, and the grease sails straight through into the duct. Push the velocity too high and you generate noise, pressure loss and re-entrainment, where grease that had been captured gets torn off the vanes again. DW172 gives the velocity ranges to design within, and the honest way to use them is to size the number and dimensions of filters to the extract air volume - never the other way round, and never by simply matching whatever was in the old canopy. If you are replacing filters and they never seem to come clean no matter how hard the kitchen scrubs, poor velocity and the wrong filter type are usually the reason, a problem we unpack in why won't my filters come clean.
A few practical rules follow from this. Mount filters at an angle so grease drains rather than pools, and keep them high enough above the cooking surface that they are not sitting in the direct flame plume. Make sure every filter is individually removable by hand, without tools, because a filter that is a nuisance to take out is a filter that does not get cleaned. And treat the filter bank as a set: mixing sizes, leaving gaps or blanking off positions all wreck the velocity distribution you carefully calculated.
Drainage, access and the rest of the system
A grease filter does not work in isolation, and the components around it are just as much a design stage decision. Every filter needs somewhere for the grease it captures to go, so the canopy should be specified with a continuous grease drainage channel or gutter feeding a removable collection tray or cup. Leaving grease to drain onto a flat canopy surface, or into a channel with no easy way to empty it, simply moves the fire load a few centimetres and makes daily cleaning miserable. The collection point should be visible, reachable and obvious to empty, because if the kitchen team cannot see it they will not maintain it.
Access is the other design decision that pays back for decades. TR19 Grease expects the entire system - canopy, filters, the full run of ductwork and the fan - to be reachable for inspection and cleaning, which means access panels specified at sensible intervals and at every change of direction while the ceiling is still open, not cut in later at three times the cost. Bends, risers and the fan housing are where grease collects fastest, so those are exactly the places to design access into from the start. Where the extract has a long or convoluted route, this is worth resolving on the drawings rather than on site. Filters are only the visible tip of a much larger grease management strategy, and it helps to think about the whole chain - filtration, drainage, access and any secondary treatment such as odour or particulate control - as one specification; our guide to how to specify a grease management system takes that wider view.
The reason all of this belongs at design stage rather than in a later value engineering exercise is simple. Around 70% of commercial kitchen fires are linked to grease build up in extract ventilation, and the cost of retrofitting proper filters, drainage and access into a live kitchen dwarfs the cost of drawing them correctly in the first place. Specify the filter to the standards, size it to the air volume, give the grease somewhere to drain and give a cleaning team somewhere to reach, and you have designed out most of the problems the system would otherwise develop.
Questions
For most commercial extraction, stainless steel baffle filters are the better choice. They shed captured grease down the vanes into a drainage channel rather than holding it in the media like mesh, they are far easier to clean thoroughly, and they carry less fire load sitting above a flame. Mesh filters are cheaper up front but clog quickly and become a maintenance and fire risk, so they are best reserved for light duty applications.
The main reference is DW172, the BESA Specification for Kitchen Ventilation Systems, which is the industry benchmark for canopy and extract design that insurers and environmental health officers use. Alongside it, BS EN 16282-6 covers aerosol separators - grease filters - and how their efficiency is tested and classified. TR19 Grease then sets the cleaning and grease deposit limits the system must meet once it is running, so it should shape design choices too.
A baffle filter only reaches its rated capture efficiency, often quoted at around 90%, when air passes through it at the face velocity it was designed for. Too low and the air will not change direction sharply enough to fling grease onto the vanes, so it passes into the duct; too high and captured grease gets torn off again, plus you get noise and pressure loss. That is why the number and size of filters should be sized to the extract air volume using the DW172 ranges, not simply matched to the old canopy.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.