What is a Restaurant Make-Up Air Fan?

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Commercial kitchens rely on powerful exhaust systems to remove heat, grease, smoke, and odors generated during cooking. But removing large volumes of air without replacing it creates a problem: negative pressure. Make-up air fan—also called a supply fan—is the component that restores balance. Properly installed and controlled, a make-up air unit protects building systems, improves comfort, reduces energy waste, and ensures kitchen hoods perform as intended.

Why a Make-Up Air Fan Matters

When a kitchen hood exhausts air, that air has to come from somewhere. If it isn’t replaced deliberately, the kitchen and building will trend toward negative pressure. Negative pressure creates issues that affect both building performance and occupant comfort:

Doors and windows that suddenly slam shut or won’t open easily because outside air is being drawn in unpredictably.
Backdrafting of combustion appliances and exhaust systems, which can introduce dangerous gases into occupied spaces.
HVAC systems working harder to maintain temperatures as uncontrolled infiltration disturbs the designed airflow patterns.
Uncomfortable drafts, inconsistent temperatures, and increased energy consumption.

Make-up air fan replaces the exact volume of air being exhausted by the kitchen hood. This balance keeps the ventilation system operating as intended and reduces wear and tear on both the hood exhaust and the building’s heating and cooling systems.

What a Make-Up Air Unit Actually Does

A make-up air unit performs one simple but vital role: it brings fresh air into the space from which contaminated air is being exhausted. In a commercial kitchen, that means the fresh air either enters directly into the kitchen or is introduced into makeup air plenum(s) that feed the hood and the space. The supply fan pushes the incoming air at rates designed to match the exhaust fan’s cfm (cubic feet per minute).

There are variations in how makeup air is delivered:

Plain supply fans that bring in unconditioned outside air.
Units with heating (electric, gas-fired, or indirect-fired) to temper incoming air and prevent cold drafts in winter.
Tempering or energy-recovery options that reduce the net energy cost associated with conditioning outside air.

Make-up air configuration depends on kitchen size, exhaust volume, local codes, and the building’s HVAC integration strategy. In many cases, the make-up air system is interlocked with the hood exhaust system so that when the hood runs, the makeup air comes on automatically at the appropriate rate.

Code Requirements and Why “Required” Matters

Building and mechanical codes commonly require makeup air for commercial kitchen exhaust systems. That requirement stems from safety and performance concerns. If a powerful exhaust hood operates without a matched supply, it creates negative pressure that can cause harmful crossflows, impair HVAC performance, and create unsafe conditions for combustion appliances.

EMCO advises designers, contractors, and restaurant operators to assume that any substantial kitchen exhaust—especially high-volume hood systems—will need a dedicated make-up air source. Local authorities may have additional rules about how the makeup air is conditioned, where it is introduced, and whether interlocks and heat safety controls are required. Consulting with a qualified mechanical professional during design avoids costly retrofits and code compliance headaches later.

Sizing and Balancing: Getting the CFM Right

Sizing a make-up air unit is straightforward in principle: it should provide a comparable volume of air to what the hood exhausts, measured in cfm. In practice, several factors influence the final specification:

The total exhaust cfm of all hood zones combined.
Whether the makeup air will be delivered directly to the hood plenum or distributed into the kitchen space.
Losses caused by ductwork, filters, and dampers that reduce delivered airflow.
Need for tempered or heated supply air to prevent discomfort or freezing in cold climates.
Local code allowances for make-up air rates and exceptions.

EMCO Utah recommends working with an experienced HVAC engineer or technician to determine the precise cfm requirement and to design an effective control strategy. Proper balancing ensures the hood has enough make-up air for capture and containment, while preventing over-pressurization that could push kitchen contaminants into adjoining spaces.

Controls and Interlocks

Controls are critical. A typical approach is an interlock between the hood exhaust fan and the make-up air unit so that the supply starts when the hood runs. More advanced systems use variable frequency drives (VFDs) or modulating dampers to match the makeup supply precisely to the hood’s demand. This improves energy efficiency and hood performance.

On/Off interlocks: Basic, reliable, used where exhaust is either on or off.
Variable control (VFD): Matches supply proportionally to exhaust, useful for variable hood operation.
Thermostatic or demand controls: Include heating or tempering when outside air is too cold.

Types of Make-Up Air Systems

While the term “make-up air unit” might conjure a single image, there are multiple configurations depending on application and performance needs:

Supply-only rooftop units: Simple fans mounted on rooftops to bring in unconditioned outside air.
Tempering units: Include heating coils to warm incoming air in cold weather so staff and customers aren’t exposed to drafts.
Indirect-fired make-up air: Uses a heat exchanger so combustion products don’t mix with the supply air—preferred when a heated supply is necessary but indoor air quality must be maintained.
Direct-fired make-up air: Burns fuel in the incoming airstream; efficient but requires careful design to avoid introducing combustion products into the space.
Heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs): Recover energy from exhaust air to precondition incoming makeup air, improving efficiency.

EMCO Utah can advise on the right type of unit based on the building envelope, climate, and the kitchen’s operational profile.

Installation Considerations

Successful make-up air installation accounts for both mechanical and architectural factors:

Location of intake: Avoid locating intakes near exhaust stacks, trash areas, loading docks, or other contamination sources.
Duct routing: Minimize long, convoluted runs that increase static pressure and reduce delivered cfm.
Backdraft dampers: Prevent reverse airflow when the supply is off, protecting indoor air quality and preventing heat loss.
Noise and vibration: Rooftop fans can transmit vibration; proper mounting and isolation are important for occupant comfort.
Fire and smoke dampers: Where makeup air ducts penetrate fire-rated assemblies, appropriate dampers and assemblies are required.
Weather protection: Intake hoods and bird screens protect the system from rain, debris, and pests.

EMCO Utah advises early coordination between mechanical, architectural, and code compliance teams. Doing this in the design phase avoids clashes with rooftop equipment access, structural load limits, and aesthetic considerations.

Energy Efficiency and Comfort Strategies

Bringing in replacement air creates energy implications. Heating or cooling outside air consumes energy, so thoughtful strategies reduce operating costs while maintaining comfort:

Tempering: Heating incoming air to a moderate temperature reduces drafts and HVAC load. Tempering options range from simple electric heat strips to efficient indirect-fired heaters.
Heat recovery: HRVs or ERVs reclaim energy from exhaust air, preheating or precooling makeup air and lowering the net energy penalty.
Demand-controlled ventilation: Use sensors and controls to supply makeup air only when needed and at the right rate.
Insulation and sealing: Properly sealed ducts and insulated units reduce thermal losses.
Variable speed drives: Reduce fan energy consumption by matching speed to the actual demand.

EMCO Utah recommends evaluating lifecycle costs, not just initial equipment price. Investing in efficiency—especially for high-hour kitchens—often yields quick payback in reduced utility bills and improved comfort that supports staff productivity.

Maintenance Best Practices

Make-up air units are workhorses that need routine attention to ensure reliable performance. Recommended maintenance tasks include:

Regular filter inspections and replacement to maintain airflow and protect downstream equipment.
Fan wheel cleaning and balancing to prevent vibration and maintain efficiency.
Motor lubrication, belt inspection, and tensioning where applicable.
Verification of controls and interlocks so the supply matches hood operation.
Seasonal checks on heating elements, burners, or heat exchangers if the unit includes tempering.
Inspecting dampers, actuators, and weather protection devices for smooth operation.

EMCO Utah stresses that neglected make-up air systems can reduce hood performance, increase energy costs, and create unsafe conditions. A preventive maintenance program prolongs equipment life and maintains kitchen safety and satisfaction.

Common Problems and How to Troubleshoot Them

Certain issues tend to recur in kitchens that have improper or poorly functioning make-up air systems. Understanding these problems helps pinpoint corrective measures:

Unbalanced airflow: Symptoms include smoky kitchens, doors slamming, or HVAC heat/cool struggle. The fix often involves recalibrating the supply to match exhaust and checking for leaks or obstructions in ducts.
Cold drafts in winter: If the makeup air arrives untempered, occupants feel uncomfortable. The solution can be adding tempering or heating to the makeup air unit.
Short cycling HVAC: Large uncontrolled infiltration can cause central HVAC to behave erratically. Ensuring a dedicated, balanced makeup air source reduces this.
Odor migration: If makeup air is routed incorrectly, odors can travel to dining or other spaces. Redirecting supply and adjusting airflow patterns can correct this.
Excessive energy use: Over-sized or always-on makeup air systems waste energy. VFDs, demand controls, and heat recovery can mitigate waste.

EMCO Utah recommends systematic testing: measure exhaust and supply cfm, inspect controls and interlocks, and check for duct leaks or improper damper settings. When in doubt, a certified HVAC professional should be engaged to diagnose and resolve the issue safely.

Make-Up Air for Mobile Kitchens and Food Trucks

Even mobile kitchens need makeup air. Food trucks and mobile units often operate in confined spaces where ventilation and fresh air supply are critical. For these applications, compact rooftop make-up air units or specialized supply solutions are available.

Key considerations for mobile kitchens include:

Space constraints and compact equipment footprints.
Mounting and weatherproofing for rooftop applications on mobile units.
Power availability and efficiency due to limited onboard electrical capacity.
Integration with the vehicle’s hood exhaust for reliable interlock operation.

EMCO Utah notes that specifying the right unit for mobile kitchens requires careful attention to size, weight, and power, and often involves products engineered specifically for mobile foodservice environments.

Design Tips EMCO Utah Recommends

From years of experience with commercial ventilation projects, EMCO Utah shares practical tips that simplify design, keep costs manageable, and increase long-term reliability:

Plan make-up air early—coordinate with architectural and structural teams to reserve rooftop space and access paths.
Design makeup air capacity equal to or slightly greater than exhaust capacity, then fine-tune during commissioning.
Use interlocks and variable control strategies to match supply to demand and save energy.
Consider indirect-fired or heat-recovery options when heating incoming air is necessary to prevent discomfort or condensation.
Keep intakes away from contaminant sources and provide adequate clearance as required by codes.
Document controls and interlocks clearly so future service technicians can troubleshoot efficiently.

FAQ: Make-Up Air Units and Commercial Kitchens

What is the difference between a make-up air fan and the building HVAC system?

A make-up air fan is dedicated to replacing the air removed by exhaust systems, such as kitchen hoods. The building HVAC system conditions and distributes air for comfort across the entire building. While HVAC and makeup air systems interact, the makeup fan specifically balances exhaust to maintain safe pressure relationships and capture performance at the hood.

Are make-up air units required by code?

Codes commonly require make-up air for significant kitchen exhaust systems to prevent negative pressure issues. Local regulations vary, so designers should consult applicable mechanical and building codes early in the project. EMCO Utah recommends assuming the need for makeup air when specifying any substantial exhaust hood.

How is a make-up air unit sized?

Make-up air is sized in cfm to match the exhaust hood’s total cfm. EMCO Utah advises accounting for duct losses, filter pressure drop, and any distribution losses when specifying the fan size and motor. Commissioning measurements and adjustments further refine the delivered airflow.

Can makeup air be heated or tempered?

Yes. Tempering or heating incoming air prevents cold drafts and improves comfort. Options include electric heat, indirect-fired heating, and heat recovery. The selection depends on climate, energy costs, and indoor air quality considerations.

What control strategies are best for energy efficiency?

Variable speed drives and demand-controlled ventilation deliver the best energy performance by matching supply to actual hood needs. Interlocks ensure makeup air runs when the hood runs, and advanced controls can modulate supply proportionally to exhaust to minimize wasted energy.

How often should makeup air units be maintained?

EMCO Utah recommends routine inspections at least twice a year, with filter checks performed more frequently depending on local air quality. Annual preventive maintenance on motors, belts, controls, and heating components preserves efficiency and reliability.

Who should be called to design or service a make-up air unit?

Certified commercial HVAC contractors or mechanical engineers experienced in kitchen ventilation should design and service makeup air systems. For project assistance or maintenance support, contact EMCO Utah at 435-256-8483.

Conclusion

A make-up air fan is more than an accessory—it’s an essential part of a safe, efficient, and comfortable commercial kitchen ventilation system. By replacing the air the hood exhausts, makeup air units prevent negative pressure, protect HVAC performance, improve occupant comfort, and reduce undue wear on equipment. EMCO Utah advises thoughtful specification, proper controls, and regular maintenance to ensure that a kitchen’s make-up air solution performs reliably for years.

Designers and operators should approach make-up air with the same care given to hood selection and exhaust design. Proper coordination during the planning stage prevents operational headaches and supports compliance with code and performance expectations.

For expert guidance on specifying, installing, or maintaining make-up air systems for commercial kitchens or mobile foodservice units, contact EMCO Utah at 435-256-8483.