When is makeup air required for a commercial kitchen hood in California?

California Mechanical Code (CMC) Section 508 requires makeup air whenever kitchen exhaust exceeds 400 CFM. This threshold is met by virtually every commercial kitchen operating a Type I hood - a standard QSR charbroiler hood exhausts 1,500–3,500 CFM, well above the trigger. The CMC requires that makeup air supply at least 80% of exhaust CFM, with the remainder acceptable as transfer air from adjacent occupied spaces. Makeup air that enters the kitchen must be tempered to within 10°F of the kitchen ambient temperature when the outdoor temperature is below 50°F - which triggers the heating coil requirement in Northern California applications.

What is the California Title 24 requirement for makeup air in restaurants?

Title 24 Part 6 Section 140.9 governs commercial kitchen ventilation energy compliance. For makeup air units serving restaurant kitchens: the heating equipment in the MAU must meet minimum efficiency standards (the gas furnace or electric heating coil must comply with Title 24 equipment efficiency tables); the MAU must have an on/off interlock with the exhaust hood fan so makeup air only runs when the hood is operating; and systems over 5,000 CFM exhaust capacity may trigger demand-controlled kitchen ventilation (DCKV) requirements in Title 24 2025. The NRCC-MCH must document MAU compliance.

How much does a commercial kitchen makeup air unit cost in California?

For a new QSR installation in California: a rooftop makeup air unit sized for 1,500–2,500 CFM (typical for a fast-casual or QSR with a single cook line) runs $8,000–$18,000 installed, including the unit, rooftop curb, ductwork, electrical, and gas connection. For a retrofit on an existing restaurant that currently runs without a compliant MAU, add 20–35% for coordination labor, ceiling penetrations, and structural support for new rooftop equipment. Units over 3,000 CFM or with high-efficiency heat recovery add $5,000–$15,000 to the equipment cost.

Can a California restaurant use recirculating air instead of outside makeup air?

Generally no for Type I hood applications. California Mechanical Code Section 511.1 prohibits recirculating grease-laden air back into the occupied space from Type I kitchen exhaust systems - the exhaust must be discharged to the exterior. Makeup air for Type I applications must be outside air or transfer air from non-contaminated adjacent spaces. Some Type II applications (dishwasher vapor exhaust, for example) may allow recirculating systems with appropriate filtration, but this requires engineering review and AHJ approval.

What documents are required for a kitchen makeup air unit permit in California?

A kitchen makeup air unit permit in California typically requires: mechanical drawings showing MAU location, CFM calculation, duct routing, and connection to the hood exhaust system; equipment cut sheet showing heating capacity, efficiency ratings, and CABEC listing; NRCC-MCH documenting Title 24 compliance for the heating equipment and the on/off interlock; structural calculations for rooftop curb loading (often needed when adding new rooftop equipment); and for Bay Area or Southern California applications, an air district permit application for combustion equipment if the MAU has a gas heating section.

Kitchen Ventilation · Energy Code · Published 2026-06-03

Commercial kitchen makeup air units: California CMC and Title 24 requirements for restaurant operators

California Mechanical Code Section 508 requires makeup air whenever kitchen exhaust exceeds 400 CFM - a threshold met by virtually every commercial kitchen. Yet improperly sized, untempered, or completely absent makeup air systems are among the most common violations found in California restaurant inspections and the primary driver of ventilation imbalance that causes summer HVAC failures. Here is what the code requires, how to calculate the right system, and what it costs.

Stainless steel commercial kitchen showing exhaust hood and ventilation system requiring California CMC makeup air compliance — Commercial kitchen ventilation in California. Every kitchen exhausting over 400 CFM requires a compliant makeup air system under California Mechanical Code §508.

What California Mechanical Code §508 requires

California Mechanical Code (CMC) Section 508 - Kitchen Ventilation - establishes the makeup air requirement for commercial kitchen exhaust systems. The rule in plain language: any kitchen exhaust system exceeding 400 CFM must be provided with makeup air equal to at least 80% of the exhaust volume. The remaining 20% can be satisfied by transfer air from adjacent conditioned spaces (typically the dining room).

The 400 CFM threshold is the dividing line between a light-use kitchenette and a commercial cooking operation. A standard QSR hood over a charbroiler typically exhausts 1,500–4,000 CFM depending on equipment load and hood size. A full-service restaurant may exhaust 3,000–8,000 CFM across multiple hood sections. Every system above 400 CFM requires a documented makeup air plan.

The CMC also requires that makeup air entering the kitchen be tempered - heated so it arrives within 10°F of the ambient kitchen temperature when the outdoor air temperature is below 50°F. In Sacramento, where winter outdoor temperatures drop to 35–40°F on many January mornings, an untempered outdoor air dump directly into the kitchen violates this requirement and creates significant discomfort for kitchen staff.

Title 24 Part 6 §140.9 - energy compliance for makeup air systems

Beyond the CMC ventilation requirement, California's energy code (Title 24 Part 6 Section 140.9) governs the energy performance of commercial kitchen ventilation systems. Key requirements:

On/off interlock: The makeup air unit must be interlocked with the exhaust hood fan - makeup air runs only when the hood is operating. A standalone MAU running 24/7 fails this requirement regardless of how efficient the unit is.
Heating efficiency: The gas heating section of the MAU must meet Title 24's minimum thermal efficiency standards. Electric heating elements must meet applicable efficiency thresholds. Equipment must be CABEC-listed.
DCKV trigger: Kitchen exhaust systems over 5,000 CFM in certain occupancy categories may trigger demand-controlled kitchen ventilation (DCKV) requirements under Title 24 2025. A DCKV-equipped system modulates fan speed based on cooking activity, reducing energy consumption 20–40%.
NRCC-MCH documentation: All of the above must be documented on the Non-Residential Certificate of Compliance - Mechanical before permit issuance.

Types of makeup air systems - and which California restaurants use each

Short-circuit (front-face) supply

Air is introduced at the front face of the hood, just inside the capture zone, directed at the cook line. Advantages: eliminates drafts across the cooking surface, reduces heating load on the MAU (the cold air doesn't have to heat the whole kitchen, just the hood zone). Disadvantages: requires careful engineering to avoid disrupting the capture velocity of the exhaust system. Common in high-end full-service restaurant applications.

Rear-discharge (back-shelf) supply

Air is discharged horizontally from a rear plenum behind the cook line equipment. Good capture performance and minimal draft. Common in QSR and fast-casual applications with linear cook lines. The rear-discharge configuration requires tight coordination with the equipment layout - no equipment can block the rear discharge slots.

Perimeter or ceiling diffuser supply

Makeup air is introduced through standard ceiling diffusers in the kitchen. Simple to install, especially on retrofit projects. Disadvantages: introduces cold drafts across the kitchen at low outdoor temperatures; may disrupt hood capture velocity if diffuser placement is not coordinated with the exhaust system design. Most common on retrofit projects where a front-face or rear-discharge system would require significant equipment modification.

Combination front-face and ceiling

Higher-volume kitchens often use a combination - short-circuit supply at the hood for the primary makeup air volume, supplemented by ceiling supply to make up the balance. This approach provides the best thermal comfort and hood performance but requires the most coordination at design stage.

How to calculate the makeup air requirement

The calculation follows directly from CMC §508:

Determine total kitchen exhaust CFM from the hood schedule and exhaust fan specifications.
Multiply by 0.80 - this is the minimum required makeup air supply volume.
Verify that the remaining 20% (transfer air from dining) is realistic - an open pass-through or a large dining-kitchen opening makes this feasible; a closed kitchen with a small service window may not support 20% transfer air without pressurizing the dining area.
Size the MAU for the 80% minimum supply volume plus any additional outside air required for kitchen ventilation under ASHRAE 62.1.
Calculate the heating load for the MAU: (CFM) × 1.1 × (indoor temp - outdoor design temp) = BTU/h required for tempering. For Sacramento (outdoor design 30°F, indoor target 70°F): 2,000 CFM × 1.1 × 40°F = 88,000 BTU/h. This is a substantial heating load - typically requiring a 90,000–125,000 BTU/h gas heater section in the MAU.

Cost ranges for California restaurant makeup air systems

Application	MAU Size	Installed Cost (NorCal)
Small QSR / fast casual (1 cook line)	1,500–2,500 CFM	$9,000–$18,000
Medium QSR / full-service (2 cook lines)	2,500–4,500 CFM	$16,000–$30,000
High-volume restaurant / ghost kitchen	4,500–8,000 CFM	$28,000–$55,000
Retrofit (existing kitchen, no MAU)	Any	Add 25–40% to above for penetrations, structural, coordination

Installed costs reflect Northern California labor rates June 2026. Southern California typically runs 8–12% higher. Costs include unit, rooftop curb, supply ductwork, gas connection, electrical, and commissioning. Does not include DCKV controls upgrade if required.

The permit sequence for a California restaurant makeup air system

Makeup air systems are permitted as part of the kitchen mechanical scope - you cannot permit the exhaust hood without addressing the makeup air in the same package. The permit sequence:

Design coordination: Mechanical engineer or C-20 contractor sizes the MAU, selects equipment, and prepares the NRCC-MCH documentation showing CMC §508 compliance and Title 24 §140.9 interlock compliance.
Simultaneous building department and health department submission: The health department reviews hood capture velocity, exhaust volumes, and kitchen layout. The building department reviews duct construction, MAU specifications, and Title 24 compliance. Submit to both at the same time. See our QSR franchise buildout guide for detailed permit timelines by county.
Installation and interlock verification: After installation, verify that the MAU on/off interlock operates correctly - hood on, MAU on; hood off, MAU off within the required time delay. Document on the CF-1R-MCH installation certificate.
Acceptance testing and commissioning: Perform a ventilation balance test - measure actual exhaust CFM and actual supply CFM. Document the balance. A system running 2,000 CFM exhaust and 1,200 CFM supply (40% short) will fail health department inspection and will create the ventilation imbalance cascade described in our guide on why restaurant HVAC fails in California summers.

Working with Sierra Mechanical

Sierra Mechanical designs, fabricates, and installs commercial kitchen makeup air systems as part of our complete kitchen ventilation scope - Type I hood, grease duct, MAU, and rooftop HVAC in a single subcontract. Our C-43 fabrication shop produces the duct transitions and plenums; our C-20 crews install the MAU, gas connection, and controls interlock.

For restaurant operators experiencing comfort complaints, high energy bills, or ventilation balance issues, our service team can perform a ventilation balance commissioning visit to measure and document your current exhaust and supply volumes. See our HVAC service agreements for preventive maintenance options. For the full NFPA 96 grease duct context, see our guide on NFPA 96 grease duct requirements for California commercial kitchens.

Request a bid at sierramechcorp.com/contact or call (916) 638-8605.

Code references: California Mechanical Code (2022) §§508, 511; California Energy Code Title 24 Part 6 (2025) §140.9; ASHRAE 62.1-2022 (ventilation for acceptable indoor air quality). Cost data current as of June 2026, Northern California market.

This article is general guidance. Specific system sizing requires engineering analysis of the kitchen equipment schedule, exhaust volumes, and building conditions by a licensed mechanical contractor.