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Kitchen extraction cleaning - diagnosis
When the canopy stops pulling as it should - smoke and steam drifting out into the kitchen instead of being drawn away - something is wrong in the extraction. The usual causes are a grease-choked system, clogged filters, a failing fan, a blockage, or a make-up air imbalance. Here is how to diagnose reduced suction at the canopy, and what each cause points to. This is general guidance.
The short answer
When the canopy stops pulling properly - you can see the smoke and steam escaping into the kitchen instead of being drawn up and away - the extraction's airflow has dropped. It's both a nuisance (a hot, smoky kitchen) and a warning (something is wrong, and a grease-choked or failing system carries a fire and reliability risk). Here's how to diagnose the cause. This is general guidance; a competent engineer can pin it down and fix it. What reduced suction looks like. The symptom is the canopy not capturing as it should: smoke, steam and cooking odours drifting out past the canopy edges into the kitchen, rather than being drawn away; the kitchen hotter, more humid, smokier. It means less air is being pulled through the system than it should be. The usual causes, in order of likelihood. Grease-choked system. The commonest cause. Grease build-up in the filters, ductwork or fan narrows the airflow path and throttles the pull - the system is simply overdue a clean. As grease accumulates, the suction gradually weakens (as covered in the airflow-dropping-off page). This is the first thing to suspect, and a good clean resolves it. Clogged or missing filters. The canopy filters, if grease-laden or blocked, strangle the intake - or if someone has removed them (a bad idea), the system loses the designed airflow path and grease goes straight into the ductwork. Check and clean (or refit) the filters. Failing or underperforming fan. The extract fan may be straining or moving less air: grease-laden (heavy with grease, out of balance), worn (bearings, motor), a slipping or broken drive belt, or an electrical fault. A fan not performing means less pull (as covered in the failing-fan pages). Check it's running and in good condition. Blockage or obstruction. A heavy grease choke, debris, or a mechanical issue (a closed or collapsed fire damper, a crushed flexible duct) can obstruct the ductwork and cut the airflow. Make-up air imbalance. Extraction needs replacement (make-up) air coming into the kitchen to pull properly. If too little comes in - a supply fan failed, windows and doors that used to be open now shut, a tightened-up building - the kitchen goes into negative pressure and the extraction is starved: it can't pull air it can't replace, so the suction drops even though nothing is wrong with the extraction itself (as covered in the make-up air page). Diagnosing which. Work through it: look at the filters and accessible ductwork (grease? blockage?); check the fan (running? straining? belt? grease-laden?); consider the make-up air (has the airflow into the kitchen changed?). The pattern points to the cause: uniform gradual decline with visible grease suggests a choked system (clean it); a fan noise or stoppage suggests the fan; a sudden change after altering doors or a supply fan suggests make-up air. The commonest answer. By far the most common cause is grease - a system overdue a clean. So the first and most likely fix for reduced suction is a good extraction clean (filters, ductwork, fan), which restores the airflow path. If suction stays poor after a proper clean, then look harder at the fan and the make-up air. So reduced suction at the canopy means the airflow has dropped - usually from grease - and diagnosing the cause (grease, filters, fan, blockage, or make-up air) points to the fix. Don't ignore it: beyond the discomfort, it often signals a system that needs cleaning or attention for fire safety and reliability. So diagnose the cause and fix the right thing - usually a clean. This is general guidance.
Key points
What it looks like
Reduced suction at the canopy shows itself as the extraction failing to capture what it should: instead of the smoke, steam, heat and cooking smells being drawn up into the canopy and away, they drift out past the canopy edges into the kitchen. The kitchen becomes hotter, more humid and smokier; the air quality drops; condensation may appear. In short, the canopy isn't pulling - the capture that should happen at the canopy line is failing, and the cooking effluent escapes.
This matters for two reasons. Immediately, it's a poor working environment (heat, steam, smoke, smells) and can breach the comfort and air-quality the extraction is there to provide. But it's also a warning sign: reduced suction means the airflow through the system has dropped, and the causes (grease, a failing fan, a blockage) often carry a fire or reliability risk. So reduced suction isn't just an annoyance to tolerate - it's a symptom to diagnose. The airflow has dropped for a reason, and finding that reason is the point. So what it looks like - smoke and steam escaping the canopy - is the symptom; the next sections work through the causes. So the canopy isn't pulling, and that has a cause. This is general guidance.
Grease and filters first
The first and commonest cause to suspect is grease - a system choked by grease build-up, overdue a clean. As grease accumulates in the filters, ductwork and fan, it narrows the airflow path and coats the fan, progressively throttling the suction. This is a gradual decline (the pull weakening over weeks and months as the grease builds), and it's exactly what a system due a clean does. The filters are the first place to look: grease-laden canopy filters strangle the intake; check whether they're clogged (or, badly, missing - which loses the designed airflow and sends grease into the duct).
So the first diagnostic step is to look at the grease: are the filters clogged? Is there visible heavy grease in the accessible ductwork and around the fan? Is the system overdue its clean? If so, grease is almost certainly the cause, and a proper extraction clean (filters, ductwork, fan) will restore the airflow path and the suction. This is the most likely answer by a wide margin - most cases of gradually reduced suction are simply a system needing cleaning. So grease and filters first - the commonest cause by far - is where diagnosis starts, and where most cases are resolved. If a good clean restores the pull, the cause was grease; if suction stays poor after a proper clean, look further (the fan, the make-up air). So suspect grease first, and clean it. This is general guidance.
The fan and blockages
If the system is clean and the suction is still poor, look at the fan and at possible blockages. The extract fan drives the whole airflow - if it's underperforming, the pull drops. A fan can underperform for several reasons: it's grease-laden (heavy with grease, out of balance, moving less air - which a clean addresses); it's worn (bearings, motor tiring with age); the drive belt is slipping or broken (a common cause of a fan spinning slowly or not at all); or there's an electrical or control fault. So check the fan: is it running? Does it sound strained, noisy or slow? Is the belt intact and tight? A fan not performing is a direct cause of reduced suction (as covered in the failing-fan pages).
A blockage or obstruction in the ductwork is the other mechanical cause: a very heavy grease choke (a section nearly closed with grease), debris or an object in the duct, a collapsed or crushed flexible duct, or a mechanical issue like a closed or dropped fire damper obstructing the run. Any of these throttles or blocks the airflow at a point. So if the filters are clear and the fan is running well but the suction is still poor, suspect a blockage somewhere in the run. So the fan and blockages - a failing fan, or an obstruction - are the causes to check once grease and filters are ruled out (or after a clean hasn't fully restored the pull). Both usually need an engineer to inspect and resolve. So check the fan, and check for obstructions. This is general guidance.
Make-up air
A cause that's easy to overlook is make-up air - the replacement air that must come into the kitchen for the extraction to pull properly. Extraction removes air from the kitchen; for it to keep pulling, an equal volume of air has to come in to replace it (through a supply/make-up air system, or through windows, doors and vents). If too little make-up air comes in, the kitchen goes into negative pressure - and the extraction is starved: it can't pull out air it can't replace, so the suction drops, even though nothing is wrong with the extraction itself.
So if the suction has dropped - especially suddenly, or after a change - consider the make-up air: has a supply/make-up air fan failed? Have windows or doors that used to be open been closed (in winter, or after building work)? Has the building been tightened up (draught-proofing, new doors) reducing the incidental air that used to come in? Any of these reduces the make-up air and starves the extraction. The fix here isn't the extraction (which may be fine) but restoring the make-up air (repairing the supply fan, providing adequate air in). This is a genuine and commonly missed cause (as covered in the make-up air page). So make-up air - the extraction needs air to pull - is a cause to consider, particularly for a sudden change or where the extraction itself checks out clean and sound. So make sure enough air is coming in. This is general guidance.
Diagnose, then fix
So diagnosing reduced suction at the canopy means working through the usual causes - grease-choked system, clogged filters, failing fan, blockage, make-up air imbalance - to find which applies, so you fix the right thing. And the practical reality is that most cases come down to grease: a system overdue a clean. So the first and most likely fix is a good extraction clean.
The sensible order is: first, suspect grease - check the filters and accessible ductwork, and if the system is due a clean (or shows visible heavy grease), get it properly cleaned (filters, ductwork, fan); this resolves most cases. If the suction stays poor after a proper clean, then look further: the fan (running well? belt? condition?), a blockage (an obstruction in the run), and the make-up air (enough air coming in?). A competent extraction engineer can diagnose across all of these and resolve it - cleaning what's choked, addressing the fan, clearing a blockage, or flagging a make-up air problem. The key is not to ignore reduced suction (it signals a real problem and often a fire/reliability risk) and not to guess (removing filters, or assuming it's the fan when it's grease) - but to diagnose and fix the actual cause. So diagnose, then fix - usually a clean, sometimes more - is how to deal with reduced suction at the canopy. So find the cause, and most often the answer is a clean. This is general guidance.
Questions
Most likely a grease-choked system overdue a clean; other causes are clogged filters, a failing fan, a blockage in the ductwork, or too little make-up air coming into the kitchen. Reduced suction means the airflow through the extraction has dropped. The commonest cause by far is grease build-up in the filters, ductwork and fan, narrowing the airflow path and throttling the pull - a system due a clean. Other causes: clogged (or missing) canopy filters strangling the intake; a failing or underperforming fan (grease-laden, worn, or a slipping belt); a blockage or obstruction in the ductwork; or a make-up air imbalance (too little replacement air coming in, starving the extraction). Diagnosis works through these. But the first and most likely answer is grease - so start by checking the filters and whether the system is due a clean. So usually grease; sometimes the fan, a blockage, or make-up air. So most likely a system needing cleaning. This is general guidance.
Usually yes - grease choking the filters, ductwork and fan is the commonest cause, and a proper clean restores the airflow; but if suction stays poor after a good clean, look at the fan, a blockage, or the make-up air. In most cases, reduced suction is a grease-choked system overdue a clean: as grease builds up, it narrows the airflow path and throttles the pull, so the suction gradually weakens. A proper extraction clean (filters, ductwork, fan) removes the grease and restores the airflow - resolving most cases. So cleaning is the first and most likely fix. However, it's not the only possible cause: if a good clean doesn't restore the suction, the fan may be failing (worn, slipping belt), there may be a blockage in the ductwork, or the make-up air may be inadequate (starving the extraction). So start by cleaning (the likeliest fix), and if the pull stays poor, diagnose further. So usually yes, cleaning fixes it - but not always. So usually a clean; sometimes more. This is general guidance.
Yes - the extraction needs make-up (replacement) air coming into the kitchen to pull properly; if too little comes in, the kitchen goes into negative pressure and the extraction is starved, so the suction drops even if the extraction itself is fine. Extraction removes air from the kitchen, and an equal volume has to come in to replace it (make-up air, through a supply system or windows, doors and vents). If too little make-up air comes in - a failed supply fan, windows and doors that used to be open now shut, a tightened-up building - the kitchen goes into negative pressure, and the extraction can't pull out air it can't replace. So the suction drops, even though nothing is wrong with the extraction itself. This is a genuine and commonly missed cause, especially where the suction dropped suddenly or after a change. The fix is restoring the make-up air, not the extraction. So yes - inadequate make-up air starves the extraction. So yes, too little air in weakens the pull. This is general guidance.
No - removing the canopy filters is a bad idea: they're part of the system, and taking them out sends grease straight into the ductwork, creating a worse fire risk; if the filters are clogged, clean or replace them instead. It can be tempting, when the filters are grease-laden and the suction is poor, to remove them - but don't. The canopy filters (baffle or mesh) are there to catch grease before it enters the ductwork; without them, grease goes straight into the duct and fan, building up far faster and creating a serious fire risk in the hidden ductwork. Removing the filters also disturbs the designed airflow. If the filters are clogged and strangling the intake, the right answer is to clean them (regularly - they're designed to be cleaned) or replace them if damaged - not to remove them. So keep the filters in and keep them clean. So no - clean or replace them, don't remove them. So no; that creates a worse problem. This is general guidance.
Check whether the fan is running and how it sounds and performs - a fan that's not running, running slowly, straining, noisy, or has a slipping or broken belt is moving less air; if the system is clean but the pull is still weak, the fan is a prime suspect. The extract fan drives the whole airflow, so a fan not performing directly cuts the suction. Signs the fan is the cause: it's not running at all (electrical fault, tripped, seized); it's running slowly or straining (a slipping or worn drive belt, tiring bearings or motor); it's noisy or vibrating (grease-laden and out of balance, or a bearing problem); or the suction is weak despite the filters and ductwork being clean. So if a proper clean hasn't restored the pull, check the fan: is it running, and does it sound and perform right? A competent engineer can test the fan's performance. Fixing it may mean a clean of the fan, a new belt, or a repair. So check the fan is running well; if the clean system still won't pull, suspect the fan. So a straining, slow or stopped fan points to itself. This is general guidance.
It's worth acting on - beyond the smoky, hot kitchen, reduced suction usually signals a grease-choked or failing system, which carries a fire and reliability risk; diagnose and fix the cause rather than tolerating it. Reduced suction is both a nuisance and a warning. The immediate effect is a poorer kitchen environment (smoke, steam, heat and smells escaping into the room, poorer air quality). But more importantly, it usually signals an underlying problem: most often a grease-choked system (a fire risk, and overdue a clean), or a failing fan or blockage (reliability risks, heading toward a breakdown). So weak suction is a symptom telling you the airflow has dropped for a reason - and that reason often matters for fire safety and reliability. So don't just tolerate it: diagnose the cause (usually grease - get it cleaned) and fix it. Acting promptly resolves the discomfort and addresses the underlying risk before it worsens. So yes, act on it - it usually signals a system needing attention. So worth acting on, not ignoring. This is general guidance.
Reduced suction is most often a grease-choked system overdue a clean. We clean the whole extraction - filters, ductwork and fan - to TR19 Grease, restoring the airflow path, and can flag a fan or make-up air problem if the pull stays poor. Ask us to diagnose and restore your canopy's suction. This is general guidance.
