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Kitchen extraction cleaning - airflow
Smoke and steam should be drawn away and cleared quickly during service. If instead they hang around - lingering in the kitchen, clearing slowly, leaving a haze - the extraction usually isn't moving enough air to remove them. That points to a choked duct, a weak or failing fan, or a lack of make-up air. Here is why smoke lingers, and what to check. This is general guidance.
The short answer
During service, the extraction should draw smoke, steam and heat away from the cooking and clear them quickly - keeping the kitchen clear to work in. If instead smoke hangs around - lingering, clearing slowly, leaving a haze in the air - the extraction isn't moving enough air to remove it. Here's why, and what to check. This is general guidance. What lingering smoke means. Smoke that hangs around means the air isn't being extracted fast enough. The system's whole job is to move air - pulling the smoke-laden air up and out, and (with make-up air) replacing it with fresh. If the smoke lingers, that air movement is too weak: the system isn't shifting enough air to carry the smoke away and clear the space. So lingering smoke is fundamentally an airflow problem - not enough air being moved. Three causes. Weak airflow comes down to one or more of three things. A choked duct (commonest). Grease builds up inside the ductwork over time, narrowing the bore. A narrower duct throttles the airflow - less air can pass through it - so less smoke is drawn away, and the smoke lingers. This is the commonest cause, because grease build-up is gradual and easy to miss until the airflow's noticeably down. And it's the most fixable: cleaning the duct restores the bore and the airflow. A weak or failing fan. The extract fan is what pulls the air through the system. If it's underpowered for the kitchen, worn, grease-laden (grease on the fan unbalances and slows it), or failing, it can't move enough air - so the smoke isn't cleared. A fan problem starves the whole system of the pull it needs. A lack of make-up air. Extraction can only pull air out if replacement air can come in - you can't remove air from a sealed box. So the kitchen needs make-up air: fresh air coming in (through a supply system, or vents/doors) to replace the extracted air. If the kitchen's sealed up - doors and windows shut, no make-up air supply - the extraction is starved: it can't pull air out because none can come in, so the smoke stays. This one's often overlooked. How this differs from smoke escaping at the canopy. This is different from smoke escaping (spilling out) at the canopy. There, the smoke isn't being captured at the hood - it spills out into the kitchen before the system even gets it (covered in the why smoke escapes the canopy page). Here, the smoke may be captured but then not cleared - it's drawn in but hangs in the space because the system isn't removing air fast enough to clear it. Escaping is a capture problem at the hood; lingering is a removal problem in the system. Both point to underperforming extraction, but at different stages. What to check. The commonest and most fixable cause is the choked duct - so lingering smoke is often a sign the ductwork needs cleaning (which restores the airflow). So the first thing to check is the duct's grease level (via a survey or inspection) and to have it cleaned to the TR19 Grease standard. Also worth checking: the fan (is it running properly, is it grease-laden, is it powerful enough) and the make-up air (is fresh air able to get in, or is the kitchen sealed). The takeaway. So smoke hanging around during service is a warning that the extraction is underperforming - not moving enough air to clear the smoke. The commonest cause is a grease-choked duct, so start by having the ductwork checked and cleaned - and check the fan and make-up air too. So don't put up with a smoky kitchen: lingering smoke means the extraction needs attention. This is general guidance.
Key points
What lingering smoke means
Smoke that hangs around during service means the air isn't being extracted fast enough. The extraction's whole job is to move air - pulling the smoke-laden, steamy, hot air up and away from the cooking and out of the building, and (with make-up air coming in) keeping fresh air moving through the space. If the smoke lingers instead of clearing, that air movement is too weak: the system isn't shifting enough air to carry the smoke away and clear the kitchen.
So lingering smoke is, at root, an airflow problem - not enough air being moved. The smoke is a visible marker of the air: if the smoky air isn't being cleared, the air isn't being moved. So when you see smoke hanging around, read it as the extraction underperforming on airflow. The question is then why the airflow is weak - which comes down to three things (the duct, the fan, the make-up air), covered next. So what lingering smoke means - the air isn't being removed fast enough - is the diagnosis: it's an airflow shortfall. The causes follow. So lingering smoke signals weak airflow. This is general guidance.
A choked duct
The commonest cause of weak airflow - and so of lingering smoke - is a grease-choked duct. Grease builds up inside the ductwork over time, coating the walls and narrowing the bore (the internal cross-section the air flows through). A narrower duct throttles the airflow: less air can pass through a constricted duct, so less smoke-laden air is drawn away, and the smoke lingers in the kitchen instead of clearing.
This is the commonest cause for two reasons. It's gradual: grease builds up slowly, so the airflow drops off gradually and is easy to miss until the smoke's noticeably hanging around. And it's hidden: the grease is inside the ductwork, out of sight, so you don't see the cause - only the effect (the lingering smoke). It's also the most fixable cause: cleaning the duct (to the TR19 Grease standard) removes the grease, restores the bore, and restores the airflow - so the smoke clears properly again. So a choked duct - the commonest cause of weak airflow - is the first thing to suspect when smoke hangs around: grease narrowing the duct is throttling the air. Cleaning the duct is usually the fix. So a grease-choked duct is the usual culprit. This is general guidance.
A weak or failing fan
The second cause is a weak or failing extract fan. The fan is what pulls the air through the whole system - it's the engine of the extraction. If the fan can't move enough air, the smoke isn't cleared, however clear the duct. A fan can be weak or failing for several reasons: underpowered for the kitchen (too small a fan for the cooking volume and duct length); worn (an old fan losing performance); grease-laden (grease built up on the fan blades unbalances and slows it, and reduces its efficiency); or failing (a motor or bearing problem).
So if the smoke lingers and the duct's reasonably clear, the fan is worth checking: is it running properly, is it grease-laden (needing cleaning), is it powerful enough for the kitchen. A fan problem starves the whole system of the pull it needs - so no amount of clear ductwork helps if the fan isn't moving the air. (Grease on the fan is itself part of the extraction cleaning - the fan is cleaned along with the duct in a full clean.) So a weak or failing fan - not enough pull to clear the smoke - is the second cause to check: the fan is the system's engine, and a weak one can't clear the smoke. So check the fan is pulling properly. This is general guidance.
A lack of make-up air
The third cause - often overlooked - is a lack of make-up air. Extraction can only pull air out of the kitchen if replacement air can come in. You can't keep removing air from a sealed box - once you've pulled some out, the pressure drops and the extraction stalls, unless fresh air flows in to replace it. So the kitchen needs make-up air: fresh air coming in (through a dedicated make-up air supply system, or through vents, doors and windows) to replace the air being extracted.
If the kitchen's sealed up - doors and windows shut, no make-up air supply, or an inadequate one - the extraction is starved: it can't pull air out because none can come in to replace it. So even with a clear duct and a strong fan, the airflow is throttled by the lack of incoming air, and the smoke hangs around. This one's easy to miss because it's not a fault in the extraction itself - it's the air supply feeding it. So it's worth checking whether fresh air can actually get into the kitchen, especially if the smoke got worse after the space was sealed up or draught-proofed. So a lack of make-up air - air can't go out if none comes in - is the third cause: without incoming air, the extraction is starved whatever its condition. So check air can get in, not just out. This is general guidance.
Lingering vs escaping
It's worth distinguishing lingering smoke from smoke escaping at the canopy, because they're different problems at different stages. Smoke escaping (spilling out) at the canopy means the smoke isn't being captured at the hood - it spills out into the kitchen before the system even draws it in (covered in the why smoke escapes the canopy page - a capture problem at the hood, from an undersized canopy, too much cooking, or weak capture). Lingering smoke here means the smoke may be captured but then not cleared - it's drawn in, but hangs in the space because the system isn't removing air fast enough.
So escaping is a capture problem at the hood (the smoke never gets properly into the system); lingering is a removal problem in the system (the smoke gets in but isn't cleared). Both point to underperforming extraction, but at different points: one at the mouth of the system, one through the system. In practice they can overlap (a badly choked duct can cause both - weak airflow means poor capture and poor clearing), and the underlying fixes overlap too (clean the system, check the fan and air). But it helps to know which you're seeing: is the smoke spilling out at the hood (escaping), or being drawn in but not clearing (lingering). So lingering vs escaping - not clearing versus not being caught - clarifies the symptom: both signal underperformance, addressed by checking the system. So identify which, then check the extraction. This is general guidance.
Questions
Because the extraction isn't moving enough air to remove it - the smoke is drawn in but not cleared fast enough; that weak airflow usually comes from a choked duct, a weak fan, or a lack of make-up air, with the choked duct the commonest. Smoke hangs around during service when the extraction isn't moving enough air to remove it. The system's job is to pull the smoke-laden air up and out and clear the space; if the smoke lingers, that air movement is too weak - the system isn't shifting enough air to carry the smoke away. Weak airflow comes down to one or more of three things. A choked duct (commonest): grease built up inside the ductwork narrows it, throttling the airflow, so less smoke is drawn away. A weak or failing fan: the fan pulls the air through, and if it's underpowered, worn, grease-laden or failing, it can't move enough air. A lack of make-up air: extraction can only pull air out if replacement air can come in, so a sealed-up kitchen starves the system. The commonest and most fixable is the choked duct. So lingering smoke means weak airflow, usually a grease-choked duct. So because the air isn't being extracted fast enough. This is general guidance.
Usually it's the commonest cause - grease built up inside the ductwork narrows the bore and throttles the airflow, so less smoke is drawn away and it lingers; cleaning the duct restores the bore and airflow, so it's the first thing to check. Usually yes - a dirty (grease-choked) duct is the commonest cause of a kitchen that stays smoky. Grease builds up inside the ductwork over time, coating the walls and narrowing the bore (the space the air flows through). A narrower duct throttles the airflow - less air can pass - so less smoke-laden air is drawn away, and the smoke lingers instead of clearing. It's the commonest cause because it's gradual (grease builds slowly, so the airflow drops off unnoticed) and hidden (the grease is inside the duct, out of sight). And it's the most fixable: cleaning the duct to the TR19 Grease standard removes the grease, restores the bore, and restores the airflow - so the smoke clears properly again. So a dirty duct is the first thing to suspect and check when the kitchen stays smoky. Other causes (the fan, make-up air) are worth checking too, but start with the duct. So usually yes - a choked duct is the likeliest cause. So yes, commonly; get the duct checked. This is general guidance.
Yes - the fan pulls the air through the system, so a fan that's underpowered, worn, grease-laden or failing can't move enough air to clear the smoke; if the duct's reasonably clear, check the fan is running properly and isn't grease-laden. Yes - the extract fan can be why smoke doesn't clear. The fan is what pulls the air through the whole system - it's the engine of the extraction - so if it can't move enough air, the smoke isn't cleared, however clear the duct. A fan can be weak or failing for several reasons: underpowered for the kitchen (too small for the cooking volume and duct length); worn (an old fan losing performance); grease-laden (grease on the fan blades unbalances and slows it, cutting its efficiency); or failing (a motor or bearing problem). So if the smoke lingers and the duct's reasonably clear, check the fan: is it running properly, is it grease-laden and needing cleaning, is it powerful enough for the kitchen. A fan problem starves the whole system of pull, so a clear duct alone won't fix it. Grease on the fan is cleaned as part of a full extraction clean. So yes - check the fan is pulling properly. So yes; a weak or grease-laden fan can be the cause. This is general guidance.
Make-up air is fresh air coming into the kitchen to replace the air being extracted; extraction can only pull air out if air can come in, so a sealed-up kitchen with no make-up air starves the extraction and the smoke stays - so check air can get in, not just out. Make-up air is fresh air coming into the kitchen to replace the air the extraction is pulling out. It matters because extraction can only pull air out if replacement air can come in - you can't keep removing air from a sealed box (the pressure drops and the extraction stalls). So the kitchen needs make-up air flowing in: through a dedicated make-up air supply system, or through vents, doors and windows. If the kitchen's sealed up - doors and windows shut, no make-up air supply, or an inadequate one - the extraction is starved: it can't pull air out because none can come in to replace it. So even with a clear duct and a strong fan, the airflow is throttled and the smoke hangs around. This cause is easy to miss because it's not a fault in the extraction itself - it's the air supply feeding it. So it's worth checking whether fresh air can actually get into the kitchen, especially if the smoke worsened after the space was sealed or draught-proofed. So make-up air is the incoming air extraction needs; without it, air can't go out. So it's the replacement air - vital for extraction to work. This is general guidance.
Escaping smoke spills out at the hood because it isn't captured (a capture problem at the canopy); lingering smoke is captured but not cleared, hanging in the space because the system isn't removing air fast enough (a removal problem in the system) - different stages, both underperformance. Lingering smoke and smoke escaping the canopy are different problems at different stages. Smoke escaping (spilling out) at the canopy means the smoke isn't being captured at the hood - it spills out into the kitchen before the system draws it in (a capture problem at the hood, from an undersized canopy, too much cooking, or weak capture - covered in the why smoke escapes the canopy page). Lingering smoke means the smoke may be captured but then not cleared - it's drawn in but hangs in the space because the system isn't removing air fast enough (a removal problem in the system). So escaping is a capture problem at the hood (the smoke never gets properly into the system); lingering is a removal problem in the system (the smoke gets in but isn't cleared). Both signal underperforming extraction, but at different points. They can overlap (a badly choked duct causes both) and the fixes overlap (clean the system, check the fan and air). So they're related symptoms of the same underperformance, at the mouth of the system versus through it. So one is not caught; the other is caught but not cleared. This is general guidance.
Read it as underperforming extraction and start with the duct - have the ductwork surveyed and cleaned to TR19 Grease (the commonest, most fixable cause); also check the fan is running properly and not grease-laden, and that make-up air can get into the kitchen. If smoke hangs around during service, read it as a warning that the extraction is underperforming - not moving enough air to clear the smoke - and act on it. Start with the duct: the commonest and most fixable cause is a grease-choked duct, so have the ductwork surveyed or inspected for its grease level and cleaned to the TR19 Grease standard, which restores the bore and the airflow. Then check the fan: is it running properly, is it grease-laden (needing cleaning as part of the clean), is it powerful enough for the kitchen. And check the make-up air: can fresh air actually get into the kitchen to replace the extracted air, or is the space sealed up. In practice, a full extraction clean addresses the commonest cause (the duct) and the fan grease at once, and a survey can flag the fan capacity and make-up air issues. So the action is: get the system surveyed and cleaned, starting with the duct, and check the fan and air supply. So don't put up with a smoky kitchen - get the extraction checked. So start with a duct clean, then check the fan and air. This is general guidance.
Smoke that hangs around during service usually means weak airflow - most often a grease-choked duct; we survey the system and clean it to TR19 Grease, restoring the duct bore and the airflow so smoke is cleared properly, and check the fan and capture along the way. Ask us to check your extraction. This is general guidance.
