A commercial kitchen needs make-up air because exhaust hoods remove large volumes of air from the space, and that air has to be replaced from somewhere. Without a proper make-up air system, the kitchen develops negative pressure, which can pull conditioned air from the rest of the building, make exterior doors difficult to open, cause gas appliances to back-draft, and significantly reduce how well the exhaust hood actually performs. Understanding this relationship is the first step toward planning a proper Make-Up Air Unit installation that matches your kitchen’s exhaust system rather than treating it as an afterthought.
Make-up air is not an optional upgrade or a nice-to-have addition to a commercial kitchen. It is a functional requirement tied directly to how exhaust hoods are designed to operate, and it is treated that way under code.
What Make-Up Air Actually Does
Every exhaust hood removes a defined volume of air from the kitchen to carry away heat, smoke, steam, and grease-laden vapor. That air does not simply disappear from the building’s overall air balance. If nothing replaces it, the kitchen space develops negative pressure relative to the rest of the building and, in some cases, relative to the outside as well.
A make-up air system is designed to supply air back into the space at a rate that offsets what the exhaust hood removes, keeping the kitchen’s air pressure in balance. This is not a passive process. Make-up air systems are engineered components, sized and configured specifically to match the exhaust volume of the hood system they support.
What Happens Without Adequate Make-Up Air
When a kitchen lacks sufficient make-up air, the effects tend to show up in several interconnected ways:
Reduced exhaust hood performance. A hood system depends on a certain volume of air moving through it to function correctly. Without enough replacement air, the exhaust hood can struggle to capture and remove smoke, heat, and grease vapor effectively, even if the hood and fan themselves are functioning properly.
Difficulty opening doors. Negative pressure inside the kitchen can make exterior doors noticeably harder to open, since the difference in air pressure works against anyone trying to pull a door inward from outside.
Back-drafting of gas appliances. This is one of the more serious risks tied to inadequate make-up air. Negative pressure can pull combustion byproducts back down flues and vents from gas water heaters, furnaces, or other gas-fired equipment instead of allowing them to exhaust properly, creating a carbon monoxide risk.
Uncomfortable working conditions. Staff often notice negative pressure through drafts, temperature swings, or a kitchen that simply feels harder to work in, even before anyone identifies make-up air as the underlying cause.
Uneven conditioning throughout the building. A kitchen pulling air from surrounding spaces can throw off HVAC balance elsewhere in the building, making other areas harder to heat or cool efficiently.
These issues do not always appear immediately after a hood system is installed. In many cases, a kitchen without adequate make-up air can seem to function acceptably at first, with problems surfacing gradually as the imbalance compounds over time.
Why Make-Up Air Is a Code Requirement, Not a Suggestion
NFPA 96 and the International Mechanical Code both address make-up air as part of a properly functioning commercial kitchen exhaust system. These codes exist because negative pressure is not just an inconvenience. It is a safety issue that affects combustion appliance venting, exhaust hood performance, and indoor air quality.
A restaurant cannot legally open or continue operating if its exhaust system does not meet code, and an exhaust hood without properly balanced make-up air is treated as an incomplete system rather than a functioning one, regardless of how well the hood itself was installed.
What Determines the Right Make-Up Air Setup
There is no universal make-up air configuration that applies to every commercial kitchen. The right setup depends on several factors specific to the space:
Exhaust hood volume: The amount of air the hood system removes directly determines how much make-up air needs to be supplied to keep the space balanced.
Building envelope and construction: How tightly sealed a building is affects how much natural infiltration already contributes to air balance, which in turn affects how much mechanical make-up air is actually needed.
Climate and conditioning needs: Make-up air introduced into a kitchen needs to be tempered appropriately for the climate, since unconditioned outside air introduced at high volume can create its own comfort and equipment strain issues.
Kitchen layout and equipment placement: Where make-up air is introduced into the space, relative to the hood and cooking line, affects how effectively it supports proper airflow rather than working against it.
Because these factors vary from kitchen to kitchen, a make-up air system should be sized and designed as part of the overall exhaust system, evaluated through a real site assessment rather than applied as a standard add-on.
Why Make-Up Air Should Be Designed Alongside the Hood System
Make-up air and exhaust hood performance are directly connected, which means designing one without the other tends to create problems down the line. A hood system installed without accounting for make-up air requirements from the start often needs retrofitting later, once negative pressure issues become apparent, which is typically more disruptive and costly than integrating make-up air into the original design.
This is one of the reasons make-up air unit installation works best as part of a broader exhaust system evaluation handled by a licensed, experienced fabricator, rather than as a separate, isolated purchase. Commercial hood and exhaust work is specialized, and in several states, purchasing a commercial hood and exhaust system legally requires a company holding proper HVACR licensing.
Coordinating Make-Up Air With the Rest of a Build-Out
Make-up air installation often overlaps with HVAC work, electrical connections, and general construction happening as part of a larger kitchen build-out. It is worth being clear that coordinating those other trades and vendors across a project ultimately falls to the owner or the general contractor managing the build. A fabricator’s role is to evaluate the kitchen’s exhaust needs and design, fabricate, and install a properly balanced system, not to manage the surrounding construction schedule.
Getting the Balance Right
Make-up air exists to solve a specific, unavoidable problem: exhaust hoods remove air, and that air has to come from somewhere. Without a properly designed system to replace it, a kitchen faces reduced hood performance, safety risks from appliance back-drafting, and code compliance issues that can affect whether a restaurant is allowed to operate at all.
If you are planning a new hood system or addressing performance issues in an existing kitchen, a professional site assessment is the most reliable way to determine what your make-up air setup actually needs, based on your specific exhaust volume, layout, and building conditions.
Frequently Asked Questions
What happens if a commercial kitchen doesn’t have enough make-up air?
The kitchen develops negative pressure, which can reduce exhaust hood performance, make exterior doors hard to open, and cause gas appliances to back-draft combustion byproducts instead of venting properly, creating a carbon monoxide risk.
Is make-up air required by code for every commercial kitchen?
NFPA 96 and the IMC address make-up air as part of a properly functioning exhaust system, and requirements typically scale with the exhaust volume the hood removes. A restaurant cannot legally operate if its exhaust system, including make-up air, does not meet code.
Does make-up air need to be heated or cooled before entering the kitchen?
In most cases, yes. Make-up air introduced into a kitchen needs to be tempered appropriately for the local climate, since unconditioned outside air at high volume can create comfort issues and place additional strain on other building systems.
Can make-up air be added to an existing hood system later?
It can, but retrofitting make-up air after the fact is typically more disruptive than designing it alongside the original hood system, since it often requires reworking ductwork, air supply points, and sometimes electrical or structural elements.
How is the right make-up air volume determined?
The volume needed depends on the exhaust hood’s airflow, the building’s construction and natural infiltration, and how tightly sealed the space is. These factors are evaluated together during a site assessment rather than applied as a standard formula.
Why should make-up air be installed by the same fabricator handling the hood system?
Make-up air and exhaust hood performance are directly connected, so designing them together helps ensure proper airflow balance. A fabricator evaluating the full system is better positioned to size and place make-up air correctly than a separate, disconnected installation would allow.
