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Kitchen extraction cleaning - make-up air design
An extraction system pulls a lot of air out of a kitchen - and that air has to be replaced. Make-up air is the fresh replacement air, and it needs to be designed in from the start: balanced to the extraction, well-distributed, and ideally tempered. Get it right and the extraction works and the kitchen is comfortable; get it wrong and both suffer. Here is how make-up air should be designed into a kitchen. This is general information; ventilation design is for a competent designer.
The short answer
Make-up air is one of the most important - and most often neglected - parts of a kitchen's ventilation. Understanding how it should be designed in shows why it matters and what 'good' looks like. This is general information; the actual design is for a competent ventilation designer. What make-up air is and why it's needed. The extraction system pulls a large volume of air out of the kitchen (carrying the heat, smoke, steam and grease). That air has to be replaced - you cannot keep removing air from a space without supplying air in, or the space goes into negative pressure (a partial vacuum). Make-up air (or replacement air) is the fresh air deliberately supplied into the kitchen to replace what the extraction removes. Because the extraction moves so much air, the make-up air must be a designed-in supply, not left to leak in through gaps and doors (which causes draughts and problems). So make-up air is essential and must be designed in. How it should be designed in. Good make-up air design has three key features: (1) Balanced to the extraction. The make-up air should supply roughly the volume of air the extraction removes, so the system is in balance. Too little make-up air and the extraction is starved and the kitchen goes negative (draughts, doors hard to open, air pulled down flues); the make-up air should match the extraction (often supplying a large proportion of the extract, with the balance from adjacent spaces, per the design). So balance is the first principle. (2) Well-distributed. The make-up air should be introduced so it reaches the kitchen effectively without causing problems: not blasting in as a draught, not creating cold spots, and - importantly - not disrupting the extraction's capture at the canopy (make-up air blown across the canopy face can spoil the capture of the cooking plume). So the supply points and airflow are designed to distribute the air well. (3) Tempered. Ideally the make-up air is tempered - heated in winter (so it doesn't chill the kitchen and staff), and not excessively hot in summer (so it doesn't add to the heat). Untempered make-up air (raw outside air) can make the kitchen uncomfortable (freezing in winter, hot in summer). So tempering the make-up air keeps the kitchen comfortable. The payoff, and the cost of getting it wrong. Designed in this way - balanced, distributed, tempered - the make-up air lets the extraction work properly (not starved) and keeps the kitchen comfortable and in balance. Neglected or poorly designed, it starves the extraction and causes negative-pressure problems (draughts, doors, flue issues, and reduced extraction) - a common hidden cause of extraction and comfort problems. So make-up air should be designed into a kitchen deliberately, as a balanced, well-distributed, tempered supply integral to the ventilation. So design make-up air in properly - the extraction and the comfort depend on it. This is general information; ventilation design is for a competent designer.
Key points
Why make-up air is needed
The reason make-up air must be designed into a kitchen is simple physics: the extraction removes a large volume of air, and that air has to be replaced - you cannot keep pulling air out of a space without supplying air in. The extraction system pulls a big volume of air out of the kitchen (carrying the heat, smoke, steam and grease out). If that air is not replaced, the kitchen goes into negative pressure - a partial vacuum, as the extraction tries to pull out air that isn't being replaced. So a supply of replacement air is not optional; it is a necessity for the extraction to work.
Make-up air (or replacement air) is that fresh air, deliberately supplied into the kitchen to replace what the extraction removes. And because the volume is large, it must be a designed-in supply - a proper make-up air system delivering the air - not left to leak in haphazardly through door gaps, windows and cracks (which causes draughts, doesn't supply enough, and creates the negative-pressure problems). So make-up air is needed, and needs designing in, precisely because the extraction moves so much air that replacing it is a significant, deliberate part of the ventilation. This is the foundation: the extraction and the make-up air are two halves of one balanced system. So why make-up air is needed - you can't extract air you don't replace. So you can't extract air you don't replace. This is general information.
Balanced to the extraction
The first principle of designing make-up air in is balance: the make-up air should supply roughly the volume of air the extraction removes, so the system is in balance - enough to replace what's extracted, without over- or under-supplying. The extraction removes a certain airflow; the make-up air should supply to match it (often a large proportion of the extract as dedicated make-up air, with the remainder drawn from adjacent areas, according to the design intent and the desired pressure relationship). The goal is a balanced system where the air removed is properly replaced.
Get the balance wrong and problems follow. Too little make-up air (under-supply) is the common fault: the extraction is starved (it can't pull out air that isn't being replaced, so it under-performs), and the kitchen goes into negative pressure - causing draughts (air rushing in through every gap), doors hard to open (the vacuum holding them), and air pulled back down flues (dangerous). Too much make-up air (over-supply) can over-pressurise the kitchen and push air (and smells) into adjacent areas. So the make-up air must be balanced to the extraction - a key design calculation. This balance is the heart of good make-up air design (and a common thing to get wrong - as covered in airflow-balance-when-make-up-air-is-the-real-problem). So balanced to the extraction - enough to replace what's removed. So enough to replace what's removed is the first principle. This is general information; the balance is a design calculation.
Well-distributed
The second design principle is distribution: the make-up air should be introduced so it reaches the kitchen effectively without causing draughts, cold spots, or - importantly - disrupting the extraction's capture at the canopy. Simply dumping a large volume of air into the kitchen can cause its own problems: a strong draught where it enters, cold or uncomfortable spots, and, critically, disruption of the extraction if the make-up air is blown across the canopy face (the incoming air can spoil the canopy's capture of the rising cooking plume, pushing the vapour out from under the canopy rather than letting it be drawn in).
So the make-up air must be well-distributed: introduced through suitable supply points and at suitable velocities so it spreads into the kitchen gently and evenly, reaches where it's needed, and does not blast, chill, or disturb the canopy's capture. The design considers where and how the air is introduced (supply grilles or diffusers positioned and sized to distribute it well, and kept clear of disrupting the canopies). Good distribution means the replacement air does its job (replacing the extracted air, keeping the balance) without creating discomfort or undermining the extraction it is meant to support. So well-distributed - reaching the kitchen without causing problems - is the second principle of make-up air design. So it must reach the kitchen without causing problems. This is general information; the design is for a competent designer.
Tempered for comfort
The third principle is tempering: ideally the make-up air is conditioned - heated in winter and not excessively hot in summer - so the incoming air keeps the kitchen comfortable rather than making it worse. Make-up air is, ultimately, outside air brought in - and raw outside air can be very cold in winter or hot in summer. If a large volume of untempered outside air is supplied into the kitchen, it can make the kitchen uncomfortable: freezing draughts of cold winter air (chilling the staff, especially near the supply), or, in summer, hot outside air adding to the kitchen's heat.
So good design tempers the make-up air: heating it in winter (so the incoming replacement air is at a comfortable temperature, not chilling the kitchen), and in summer supplying air that is not excessively hot (and, in some systems, cooling it). Tempered make-up air keeps the kitchen comfortable while still doing its job of replacing the extracted air. This matters for staff comfort and for the kitchen's thermal balance year-round (untempered make-up air is a common cause of kitchens that are freezing in winter or that the make-up air makes hotter in summer). So tempered for comfort - not freezing in winter or baking in summer - is the third principle. Tempering can add cost and plant, so it is a design decision, but it is important for a comfortable kitchen. So temper the make-up air for comfort. This is general information; the design is for a competent designer.
Designed in, not left to chance
So make-up air should be designed into a kitchen deliberately - as a balanced, well-distributed, tempered supply that is integral to the ventilation - because it is the essential partner to the extraction, and getting it right is what lets the extraction work and the kitchen stay comfortable. Balanced to the extraction (so it's not starved and the pressure is right), well-distributed (so it reaches the kitchen without draughts or disrupting the canopies), and tempered (so it doesn't chill or overheat the kitchen): these are the marks of good make-up air design. So designed in, not left to chance - balanced, distributed, tempered, the extraction's partner.
The key message is that make-up air is not an afterthought but half of the ventilation system - the extraction and the make-up air are two halves of one balanced whole, and neglecting the make-up air undermines the extraction and the comfort. Many extraction and comfort problems (a starved, under-performing extraction; a kitchen full of draughts; doors hard to open; a freezing or baking kitchen) trace back to make-up air that was neglected or poorly designed. So make-up air should be designed in properly from the start (or corrected if it's the cause of problems), as an integral, balanced, distributed, tempered supply - the partner that lets the extraction do its job and keeps the kitchen comfortable. This is ventilation design, for a competent designer, but understanding it helps you recognise its importance. So design make-up air in as the extraction's balanced, distributed, tempered partner. So designed in, not left to chance. This is general information; ventilation design is for a competent designer.
Questions
It is the fresh air deliberately supplied into the kitchen to replace the large volume of air the extraction pulls out - the essential partner to the extraction, keeping the system in balance. The extraction removes a big volume of air from the kitchen (carrying the heat, smoke, steam and grease). That air has to be replaced - you can't keep pulling air out of a space without supplying air in, or it goes into negative pressure. Make-up air (or replacement air) is the fresh air supplied in to replace what the extraction removes. Because the volume is large, it should be a designed-in supply (through a make-up air system), not left to leak in through gaps and doors. So make-up air is the deliberate replacement-air supply that balances the extraction - one half of the ventilation system, essential for the extraction to work and the kitchen to be comfortable. So make-up air is the fresh replacement air balancing the extraction. This is general information.
Because without adequate make-up air the extraction is starved and the kitchen goes into negative pressure - causing draughts, doors hard to open, air pulled down flues, and reduced extraction; it is essential to the extraction working. The extraction removes a large volume of air, which must be replaced. If the make-up air is inadequate, the extraction can't pull out air that isn't being replaced - so it under-performs (starved) - and the kitchen goes into negative pressure (a partial vacuum). That causes real problems: draughts (air rushing in through every gap), doors hard to open (held by the vacuum), air pulled back down flues (dangerous), and a weakened extraction (not clearing the heat, smoke and grease properly). So make-up air is important because the extraction depends on it, and its neglect causes both extraction and comfort problems. It is a common hidden cause of such problems. So it's important because the extraction and comfort depend on it. So it's essential to the extraction and comfort. This is general information.
Enough to balance the extraction - roughly the volume the extraction removes, so the system is in balance; it is a design calculation matched to the extraction's airflow. The make-up air should supply to match what the extraction removes, so the system is balanced (the air removed properly replaced). In practice this often means supplying a large proportion of the extract airflow as dedicated make-up air, with the remainder drawn from adjacent areas, according to the design intent and the desired pressure relationship between the kitchen and neighbouring spaces. Too little starves the extraction and causes negative pressure; too much over-pressurises. So the amount is a design calculation matched to the specific extraction's airflow - done by a competent ventilation designer. The principle is balance: the make-up air supply matched to the extraction's demand. So it needs enough to balance the extraction, by design calculation. So roughly the volume the extraction removes, by design. This is general information; the amount is a design calculation.
Because make-up air blown across the canopy face can disrupt the extraction's capture - pushing the rising cooking plume out from under the canopy rather than letting it be drawn in, spoiling the extraction. The canopy captures the rising plume of heat, smoke and grease-laden vapour from the cooking by drawing it in. If make-up air is introduced so that it blows across or into the canopy face, it can disturb this capture - the incoming air pushing the plume sideways or out from under the canopy, so it escapes into the kitchen rather than being captured and extracted. So the make-up air, though needed, must be distributed so it doesn't disrupt the canopies - introduced away from the canopy faces, at gentle velocities, so it replaces the extracted air without spoiling the extraction's capture. This is a key part of good make-up air distribution design. So make-up air shouldn't blow across the canopy because it disrupts the extraction's capture. So it would spoil the canopy's capture of the plume. This is general information; the design is for a competent designer.
Ideally yes - tempered (heated in winter, not excessively hot in summer) - so the incoming replacement air keeps the kitchen comfortable rather than chilling it in winter or adding heat in summer. Make-up air is outside air brought in, which can be very cold in winter or hot in summer. Supplying a large volume of untempered outside air can make the kitchen uncomfortable - freezing draughts of cold winter air (chilling the staff), or hot air adding to the summer heat. So good design tempers the make-up air: heating it in winter so it's at a comfortable temperature, and in summer supplying air that isn't excessively hot (and sometimes cooling it). Tempered make-up air keeps the kitchen comfortable while still replacing the extracted air. Tempering adds cost and plant, so it's a design decision, but it's important for year-round comfort (untempered make-up air is a common cause of freezing or overly hot kitchens). So ideally yes - make-up air should be tempered for comfort. So yes - it should ideally be tempered. This is general information.
They are complementary - make-up air lets the extraction pull its full airflow, and keeping the extraction clean keeps the airflow unrestricted; both are needed for the ventilation to work and the kitchen to be comfortable. Make-up air and clean extraction both affect the airflow, from different ends. Make-up air ensures the extraction has replacement air so it can pull its full airflow (without it, the extraction is starved). Cleaning ensures the extraction isn't grease-choked, so it can pull its full airflow (grease-choking restricts it). So both are needed for the extraction to move its full airflow and do its job: adequate make-up air (so it's not starved) and a clean system (so it's not choked). If either is wrong - inadequate make-up air, or a grease-choked system - the extraction under-performs. So keeping the extraction clean and having good make-up air are complementary parts of a well-working ventilation system. So they're complementary - both needed for full airflow. So both keep the airflow working. This is general information.
Make-up air is the extraction's essential partner - balanced, distributed and tempered, it lets the extraction work. We keep the extraction clean so it pulls its full airflow, and a well-designed make-up air supply keeps the whole system in balance. Ask us about keeping your extraction clean and free-flowing. This is general information; ventilation design is for a competent designer.
