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Kitchen extraction cleaning - system sizing
A kitchen extraction system only works if it's sized to the cooking - enough extraction to capture the heat, smoke and grease the appliances produce, matched by enough make-up air coming in. Undersized, it can't cope; oversized, it wastes energy and unbalances the kitchen. Here is what correctly sizing an extraction system involves, and why it matters. This is general commentary on system design.
The short answer
An extraction system that's the wrong size will never work well, however well it's cleaned and maintained - so getting the sizing right at design is fundamental. Here's what sizing a kitchen extraction system correctly involves, and why both undersizing and oversizing cause problems. This is general commentary on system design; the actual sizing is a job for a competent ventilation designer. What sizing means. Sizing an extraction system means matching its capacity to the cooking it serves. The system has to move enough air to capture and remove what the appliances produce - the heat, smoke, steam and grease-laden air. So sizing involves: the extraction rate (the volume of air the system moves, matched to the cooking load - more intensive, hotter, greasier cooking needs a higher rate); the canopy (sized and positioned to cover the appliances and capture their rising plume); and the ductwork and fan (sized to move the required air volume through the system). Get these matched to the cooking, and the system can capture and remove the effluent as intended. The make-up air must match. Crucially, the extraction must be matched by enough replacement air - make-up air - coming into the kitchen. You can only extract as much air as you can replace: if the extraction rate exceeds the make-up air available, the kitchen goes into negative pressure and the extraction is starved (it can't pull air it can't replace), so it underperforms. So correct sizing isn't just the extraction - it's the extraction and the make-up air balanced together (as covered in the make-up air and airflow-balance pages). A system sized without matching make-up air won't work properly. Why undersizing fails. An undersized system can't cope with the cooking: it can't move enough air to capture the heat, smoke and grease, so the effluent escapes into the kitchen (a hot, smoky, steamy kitchen), capture fails at the canopy, and more grease deposits where it shouldn't (in the kitchen and in the wrong parts of the system). So undersizing means a system that visibly can't do its job - poor capture, poor conditions, poor performance. Why oversizing wastes. An oversized system - bigger than the cooking needs - wastes energy: a larger fan than necessary, moving more air than required, running harder and costing more to run (as covered in the hidden cost of an oversized extraction fan). It can also unbalance the kitchen: over-extracting relative to the make-up air, causing excessive negative pressure, draughts, and problems drawing air in. So oversizing isn't 'safe' - it costs money and can cause its own problems. The right size is a balance. So correct sizing is a balance: enough capacity to capture and remove the cooking's output, matched by adequate make-up air - and not more than needed. It's a genuine design calculation, based on the appliances (their type, number and heat/grease output), the canopy design, the duct route and the make-up air provision, done by a competent ventilation designer to the relevant industry guidance (the recognised ventilation standards). It's not something to guess, eyeball or copy from another kitchen - the specifics matter. The link to cleaning. Sizing connects to cleaning and maintenance: a well-sized system captures grease properly (at the canopy and filters, as intended) and performs as designed, which supports effective ongoing cleaning and airflow. A badly-sized system has inherent problems - poor capture, grease in the wrong places, imbalance - that no amount of cleaning can fix (though good cleaning still matters). So correct sizing is the foundation a cleanable, well-performing system is built on. The takeaway. So a kitchen extraction system must be correctly sized to the cooking - enough extraction to capture the heat, smoke and grease, matched by adequate make-up air, and not oversized - via a competent ventilation designer to the relevant guidance. So size it right at design; it's the foundation everything else rests on. This is general commentary on system design, not a specification for your system.
Key points
What sizing means
Sizing an extraction system means matching its capacity to the cooking it serves. The system has to move enough air to capture and remove what the appliances produce - the heat, smoke, steam and grease-laden air rising off the cooking. So sizing involves several matched elements: the extraction rate (the volume of air the system moves, matched to the cooking load - more intensive, hotter, greasier cooking needs a higher rate); the canopy (sized and positioned to cover the appliances and capture their rising plume); and the ductwork and fan (sized to move the required air volume through the whole system).
Get these matched to the cooking, and the system can do its job - capturing the effluent at the canopy and removing it through the system, keeping the kitchen's air clear and the grease contained. Sizing is therefore a design decision made when the system is specified, based on the specific cooking the kitchen will do. It's not a one-size-fits-all matter: a heavy-grilling, high-volume kitchen needs a very different size from a light one. And, as the next section covers, the extraction has to be balanced with the make-up air. So what sizing means - capacity matched to the cooking - is the core idea: the system's extraction, canopy, duct and fan all sized to handle what the appliances produce. So the system is sized to capture and remove the cooking's output. This is general commentary on system design.
Make-up air must match
A crucial part of correct sizing, often underappreciated, is that the extraction must be matched by enough replacement air - make-up air - coming into the kitchen. The physics is simple: you can only extract as much air as you can replace. If the extraction rate exceeds the make-up air available, the kitchen goes into negative pressure and the extraction is starved - it can't pull out air it can't replace - so it underperforms however well the extraction side is sized.
So correct sizing isn't just the extraction capacity in isolation; it's the extraction and the make-up air balanced together. A system designed with a high extraction rate but inadequate make-up air provision won't achieve that rate in practice (it's starved), and the kitchen suffers negative pressure, draughts and problems drawing air in (as covered in the make-up air and airflow-balance pages). So the make-up air is an integral part of sizing the system - designed in alongside the extraction, not forgotten. This is a common real-world problem: extraction that can't perform because the make-up air wasn't matched to it. So make-up air must match - you can only extract what you replace - is essential to correct sizing: the extraction and the incoming air designed as a balanced pair. So size the make-up air to match the extraction. This is general commentary on system design.
Under and oversizing
Both sizing errors cause real problems - it's not the case that bigger is safer. Undersizing fails: an undersized system can't cope with the cooking, unable to move enough air to capture the heat, smoke and grease. So the effluent escapes into the kitchen (hot, smoky, steamy conditions), capture fails at the canopy, and grease deposits where it shouldn't (in the kitchen and the wrong parts of the system). An undersized system visibly can't do its job - poor capture, poor conditions, poor performance.
Oversizing wastes: an oversized system - bigger than the cooking needs - wastes energy, with a larger fan than necessary moving more air than required, running harder and costing more to run (as covered in the hidden cost of an oversized extraction fan). It can also unbalance the kitchen, over-extracting relative to the make-up air and causing excessive negative pressure and draughts. So oversizing isn't a safe default - it costs money and can cause its own problems. The right size is a balance: enough capacity to capture and remove the cooking's output, matched by adequate make-up air, and not more than needed. So under and oversizing - both wrong sizes cause problems - is why correct sizing matters: too small fails to capture, too big wastes and unbalances. The target is the right size for the actual cooking. So aim for the right size, not the biggest. This is general commentary on system design.
A design calculation
Correct sizing is a genuine design calculation, not something to guess, eyeball or copy from another kitchen. It's based on the specifics: the appliances (their type, number, and heat and grease output), the canopy design (size, position, type), the duct route (its length and configuration), and the make-up air provision - all worked through to determine the extraction rate and the sizing of the canopy, ductwork and fan. This is done by a competent ventilation designer, to the relevant industry guidance (the recognised commercial-kitchen ventilation standards and design guidance).
So sizing an extraction system correctly is a job for a professional - a ventilation designer or specialist who can assess the kitchen and cooking, do the calculations, and design a system matched to the need (extraction and make-up air balanced, to the guidance). It shouldn't be guessed or based on a rough impression, because the specifics genuinely determine the right size, and getting it wrong (either way) causes the problems above. This page is general commentary on what sizing involves - not a specification or calculation for any particular system, which needs the professional design. So a design calculation - a job for a competent designer - is how correct sizing is achieved: assessed and calculated by a professional to the relevant standards, for the specific kitchen. So have the system sized by a competent ventilation designer. This is general commentary on system design, not a specification for your system.
Sizing and cleaning
Correct sizing connects to cleaning and long-term performance: it's the foundation a cleanable, well-performing system is built on. A well-sized system captures grease properly - at the canopy and filters, as intended - and performs as designed, which supports effective ongoing cleaning and good airflow. When the system is the right size, the grease goes where it should be caught and removed, and the cleaning and airflow work as they're meant to.
A badly-sized system, by contrast, has inherent problems that no amount of cleaning can fully fix: an undersized system lets grease deposit in the wrong places and the kitchen (poor capture); an oversized system wastes energy and unbalances the airflow. Good cleaning still matters enormously (a well-sized system still needs regular cleaning to standard), but cleaning can't compensate for a fundamentally wrong size. So sizing and cleaning work together: correct sizing gives you a system that captures and performs properly, and regular cleaning keeps it that way. So sizing and cleaning - the foundation for a system that works - means correct sizing at design is what makes a system that can then be kept clean and performing. If you have persistent capture or performance problems that cleaning doesn't resolve, sizing may be the underlying issue, worth a designer's assessment. So get the sizing right, then keep it clean. This is general commentary on system design, not a specification for your system.
Questions
Matching the system's capacity to the cooking - enough extraction to capture the heat, smoke and grease the appliances produce, with the canopy, ductwork and fan sized to move that air, and matched by adequate make-up air. Sizing an extraction system means matching its capacity to the cooking it serves. The system must move enough air to capture and remove what the appliances produce (heat, smoke, steam, grease-laden air), so sizing involves the extraction rate (matched to the cooking load), the canopy (sized to cover the appliances and capture their plume), and the ductwork and fan (sized to move the required air). Crucially, the extraction must be matched by enough make-up air coming in (you can only extract what you can replace). So correct sizing is the extraction capacity and the make-up air balanced together, matched to the cooking - not too small (which fails to capture) and not too big (which wastes energy). It's a design calculation for a competent ventilation designer. So it means capacity matched to the cooking, with make-up air. So matching the system to the cooking, balanced with make-up air. This is general commentary on system design.
Because you can only extract as much air as you can replace - if make-up air is inadequate, the kitchen goes into negative pressure and the extraction is starved, so it underperforms however well the extraction side is sized. Make-up air (the replacement air coming into the kitchen) is integral to correct sizing because of a simple physical fact: you can only extract as much air as you can replace. If the extraction rate exceeds the make-up air available, the kitchen goes into negative pressure and the extraction is starved - it can't pull out air it can't replace - so it can't achieve its designed rate, and the kitchen suffers negative pressure, draughts and problems drawing air in. So sizing the extraction without matching the make-up air produces a system that won't perform as intended. Correct sizing therefore designs the extraction and the make-up air as a balanced pair (as covered in the make-up air and airflow-balance pages). This is a common real-world problem - extraction that can't perform because the make-up air wasn't matched. So make-up air must be sized to match the extraction. So because extraction needs matching replacement air. This is general commentary on system design.
It can't cope with the cooking - it can't move enough air to capture the heat, smoke and grease, so they escape into the kitchen, capture fails at the canopy, and grease deposits where it shouldn't; the kitchen is hot, smoky and poorly served. An undersized extraction system can't cope with the cooking it serves - it can't move enough air to capture and remove the heat, smoke, steam and grease the appliances produce. The consequences: the effluent escapes into the kitchen (hot, smoky, steamy conditions, poor air quality); capture fails at the canopy (the plume isn't drawn away properly); and grease deposits where it shouldn't - in the kitchen and the wrong parts of the system - rather than being captured and removed as intended. So an undersized system visibly can't do its job: poor capture, poor working conditions, and poor performance that no amount of cleaning fixes (the capacity simply isn't there). Undersizing is a fundamental design shortfall. If your extraction can't cope with your cooking despite being clean and working, undersizing may be the issue - worth a ventilation designer's assessment. So it fails to capture, and the kitchen suffers. So it can't capture the cooking's output. This is general commentary on system design.
No - oversizing wastes energy (a bigger fan than needed, running harder and costing more) and can unbalance the kitchen (over-extracting relative to the make-up air); the right size is enough for the cooking, matched by make-up air, not more. No - bigger isn't safer or better. An oversized extraction system (bigger than the cooking needs) has its own problems. It wastes energy: a larger fan than necessary moves more air than required, running harder and costing more to run (as covered in the hidden cost of an oversized extraction fan) - an ongoing waste. And it can unbalance the kitchen: over-extracting relative to the make-up air, causing excessive negative pressure, draughts, and problems drawing air in. So oversizing isn't a safe default - it costs money and can cause its own issues. The right size is a balance: enough capacity to capture and remove the cooking's output, matched by adequate make-up air, and not more than needed. So aim for the correct size for your actual cooking, not the biggest. So no - oversizing wastes energy and unbalances. So no; the right size, not the biggest. This is general commentary on system design.
A competent ventilation designer - it's a genuine design calculation based on the appliances, canopy, duct route and make-up air, done to the relevant industry guidance, not something to guess or eyeball. Sizing an extraction system correctly is a genuine design calculation that should be done by a competent ventilation designer or specialist. It's based on the specifics: the appliances (type, number, heat and grease output), the canopy design, the duct route, and the make-up air provision - worked through to the extraction rate and the sizing of the canopy, ductwork and fan, matched together and to the relevant industry guidance (the recognised commercial-kitchen ventilation standards). It shouldn't be guessed, eyeballed, or copied from another kitchen, because the specifics genuinely determine the right size and getting it wrong (either way) causes problems. So for a new system, an upgrade, or persistent problems that might be sizing-related, involve a competent ventilation designer to assess and size it properly. This page is general commentary, not a specification for your system. So a competent ventilation designer, to the guidance. So a qualified ventilation designer. This is general commentary on system design, not a specification for your system.
No - cleaning is essential but can't compensate for wrong sizing; an undersized or oversized system has inherent capture, energy or balance problems that only correct design fixes, though a well-sized system still needs regular cleaning to perform. Cleaning and sizing are different things, and cleaning can't fix a fundamentally wrong size. A well-sized system captures grease properly and performs as designed, and regular cleaning keeps it that way - so cleaning is essential. But if a system is badly sized, it has inherent problems cleaning can't resolve: an undersized system can't capture the cooking's output (the capacity isn't there, so grease deposits in the wrong places and the kitchen); an oversized system wastes energy and unbalances the airflow. These are design faults, fixed only by correct sizing (a design matter for a ventilation designer), not by cleaning. So good cleaning still matters enormously (a well-sized system must be cleaned regularly to standard), but it works on top of correct sizing, not instead of it. If persistent capture or performance problems survive good cleaning, sizing may be the underlying issue. So no - cleaning can't fix wrong sizing; both matter. So no; correct sizing is a design matter. This is general commentary on system design, not a specification for your system.
A correctly-sized system captures grease properly and performs as designed; we clean the whole system to TR19 Grease to keep it doing so - and if persistent capture problems point to sizing, that's a matter for a ventilation designer. Ask us to keep your extraction cleaned and performing. This is general commentary on system design.
