CMC · California Mechanical Code

What makeup air is required for exhaust systems and enclosed parking garages?

Q: Are small residential garages exempt from ventilation?

An enclosed parking garage used for storage that is 1000 ft² or smaller and stores 5 or fewer vehicles is exempt from the exhaust rate requirement in § 403.7.1 . Note: other codes (e.g., energy, fire, local ordinances) may still impose requirements.

Q: Can I use CO sensors to cut fan runtime?

Yes — § 403.7.2 permits intermittent operation if the system uses approved automatic detection or CO/NO2 sensors, provided the sensors and control keep concentrations within the limits in the exceptions.

Q: What if I don’t want to use the 14,000 cfm per operating vehicle alternative?

Then size the system using the exhaust rates contained in Table 403.7 (occupancy‑specific rates). The table itself was not included in the retrieved files, so consult the actual code book or the AHJ for the table values.

Q: Do makeup‑air temperature or conditioning requirements appear here?

Section § 403.7 permits the source of makeup air but does not in the retrieved text set conditioning or temperature limits for makeup air; other sections or the energy code may control how makeup air is treated. Consult the CMC and California Energy Code for conditioning/energy requirements.

The California Mechanical Code requires that makeup air replace required exhaust (and may be outdoor, recirculated, or transfer air). Enclosed parking garages must typically have continuous mechanical ventilation unless they qualify for approved automatic or sensor control; small garages under 1000 ft² (or storing 5 or fewer vehicles) are exempt. There is an HCD alternative that sizes exhaust at 14,000 cfm per operating vehicle (operating vehicles = 2.5% of spaces), and exhaust inlets must be distributed so no point is more than 50 ft from an inlet. All of these rules are stated in **§ 403.7**, **§ 403.7.1**, and **§ 403.7.2**.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Exhaust airflow for occupancies is specified in § 403.7 of the California Mechanical Code; makeup air for exhaust systems may be provided as a combination of outdoor air, recirculated air, and transfer air. For enclosed parking garages, special rules apply: exhaust rates follow Table 403.7, small garages may be exempt, and mechanical ventilation systems for enclosed garages are generally required to operate continuously. These requirements and the parking‑garage exceptions/alternatives are in § 403.7, § 403.7.1, and § 403.7.2.

The single most important rule: provide the makeup air needed to replace required exhaust per § 403.7; for parking garages follow § 403.7.1 and § 403.7.2 (including the continuous‑operation rule and the alternative minimum exhaust provisions).

Requirements in detail

Basics (what makeup air can be)

Makeup air for required exhaust systems may be any combination of outdoor air, recirculated air, and transfer air — the CMC explicitly permits these choices. See § 403.7.

Enclosed parking garages — operation and sizing rules

Continuous operation: Mechanical ventilation systems for enclosed parking garages must operate continuously unless one of the listed exceptions applies. See § 403.7.2.
Small‑garage exemption: No exhaust rate is required for an enclosed parking garage that has a floor area of 1000 square feet (92.9 m2) or less and is used for the storage of 5 or fewer vehicles. See § 403.7.1.
Automatic/intermittent operation permitted: Systems may run intermittently if they are automatically controlled by approved detection (vehicle operation or occupant presence). Approved CO/NO2 sensing devices may modulate ventilation subject to concentration limits (see exceptions to § 403.7.2).

Alternative minimum exhaust and inlet distribution (HCD rules)

Alternative minimum exhaust capacity (HCD): In lieu of the exhaust rates in Table 403.7, ventilation systems for enclosed garages can be designed so they are capable of providing 14,000 cfm (6608 L/s) of exhaust air for each operating vehicle. The number of “operating vehicles” is determined as 2.5% of all parking spaces, not less than one. See § 403.7.2.2.
Exhaust inlet distribution: Where multiple exhaust inlets are used, design must ensure that no portion of the parking garage is more than 50 feet (15 240 mm) from an exhaust inlet, and that the highest elevation of each exhaust inlet is no greater than 12 inches (305 mm) below the lowest ceiling level. See § 403.7.2.3.

Sensor modulation limits (exceptions to continuous operation)

Approved automatic carbon monoxide and nitrogen dioxide detectors may modulate ventilation. The detectors are limited to a maximum average of 50 ppm CO (8‑hour avg) or 1 ppm NO2 (8‑hour avg), with permitted short spikes of 200 ppm CO or 5 ppm NO2 for periods not exceeding 15 minutes. See exceptions to § 403.7.2.

Decision‑relevant values (quick reference table)

Item	Decision value / threshold	Code reference
Makeup air allowed as	Combination of outdoor air, recirculated air, transfer air	§ 403.7
Small enclosed garage exemption	≤ 1000 ft² (92.9 m²) and ≤ 5 vehicles stored	§ 403.7.1
Garage ventilation operation	Continuous (unless allowed automatic/intermittent control)	§ 403.7.2
Alternative exhaust capacity (HCD)	14,000 cfm (6608 L/s) per operating vehicle; operating vehicles = 2.5% of spaces, min 1	§ 403.7.2.2
Exhaust inlet spacing	No point > 50 ft (15 240 mm) from an inlet	§ 403.7.2.3
Exhaust inlet elevation	Inlet highest elevation ≤ 12 in (305 mm) below lowest ceiling level	§ 403.7.2.3
CO / NO2 sensor modulation limits	50 ppm CO (8‑hr avg); 200 ppm CO (≤15 min); 1 ppm NO2 (8‑hr avg); 5 ppm NO2 (≤15 min)	Exception to § 403.7.2
Exhaust rates for other occupancies	See Table 403.7 (table text not provided here)	§ 403.7

Note: the numeric exhaust rates for occupancies other than garages appear in Table 403.7; the table text itself was not included in the retrieved material and therefore is not reproduced here.

Exceptions & special cases

Small enclosed garages used only for storage and meeting the area/vehicle limit (≤ 1000 ft² and ≤ 5 vehicles) are not required to provide the Table 403.7 exhaust rate. See § 403.7.1.
Continuous operation requirement may be replaced by automatic or sensor‑based intermittent operation when the system is designed to activate on vehicle operation or occupant presence, or when approved CO/NO2 sensors are used within the concentration limits shown in the exceptions to § 403.7.2.
If you choose the HCD alternative (the 14,000 cfm per operating vehicle option), you must size exhaust inlets so no point is more than 50 ft from an inlet and meet the inlet elevation requirement in § 403.7.2.3.

Common mistakes

Assuming makeup air must be 100% outdoor air. The CMC permits a combination of outdoor, recirculated, and transfer air for makeup (see § 403.7).
Overlooking the small‑garage exemption: designers sometimes apply Table 403.7 rates even when the garage qualifies for the ≤1000 ft² / ≤5 vehicles exemption in § 403.7.1.
Forgetting the continuous‑operation requirement for enclosed garages — or failing to include approved controls when designing intermittent operation under the exceptions to § 403.7.2.
Relying on a local practice or a single sensor without confirming the sensor types and alarm/setpoint limits called out in the code exceptions; the CMC requires approved devices and specific concentration limits for modulation.
Not checking Table 403.7: many exhaust rates for occupancies are in that table (text not available in the retrieved file); do not assume rates without consulting the table.

Worked example — concrete scenario

Scenario: You are designing ventilation for an underground enclosed parking garage with 200 parking spaces. You plan to use the HCD alternative in § 403.7.2.2.

Determine the number of “operating vehicles”:
- Operating vehicles = 2.5% × 200 = 5 vehicles (code requires not less than 1).
Use the alternative minimum exhaust capacity:
- Exhaust capacity required = 14,000 cfm per operating vehicle × 5 vehicles = 70,000 cfm total. § 403.7.2.2.
Inlet distribution:
- Design exhaust inlet locations so no portion of the garage is more than 50 ft from an inlet, and position inlet highest elevations ≤ 12 in below the lowest ceiling level, per § 403.7.2.3.
Operation & controls:
- Because enclosed garages generally must run continuously (§ 403.7.2), either operate the fans continuously or provide approved automatic detection or CO/NO2 sensors and control logic that meet the exception limits. If using sensors, ensure detectors are approved and the modulation keeps averages and short‑term peaks within the code limits.

(If you elect instead to design to the exhaust rates in Table 403.7, use the applicable per‑occupancy rate from that table — the table itself was not present in the retrieved file.)

Related provisions

§ 403.7 (Exhaust ventilation; makeup air allowed as outdoor/recirculated/transfer air)
§ 403.7.1 (Parking garage exhaust — exemption for small garages)
§ 403.7.2 (Enclosed parking garages — continuous operation and exceptions)
§ 403.7.2.2 (Alternative minimum exhaust rate — HCD)
§ 403.7.2.3 (Exhaust inlet distribution and elevation)
§ 403.8 (Dynamic reset of outdoor intake/zone airflow — relevant when coordinating exhaust and makeup air performance)
§ 701.3 (Makeup air — when exhaust interferes with appliance operation) — CMC Chapter 7 on combustion air (relevant when garages contain appliances)

If you need, I can:

Locate and extract the actual numeric exhaust rates from Table 403.7 (the table text was not included in the retrieved files), or
Produce a ventilation sizing worksheet for a specific garage (include area, number of spaces, expected occupancy modes, and climate).

Code references

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

CMC § 403.6.1 High relevance — show source text
T = 3 v/Vbz (Equation 403.6.1)

Where:

T = averaging time period, minutes.

v = the volume of the ventilation zone where averaging is being applied, ft [3] (m [3] ).

Vbz = the breathing zone outdoor airflow calculated in accordance with Equation 403.2.1 and design value of the zone population ( Pz ), cubic foot per minute (CFM).

For SI Units: 1 cubic foot = 0.0283 m [3], 1 cubic foot per minute =

0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s

Acceptable design adjustments based on this optional provision including the following:

(1) Zones with fluctuating occupancy: The zone population ( Pz ) shall be permitted to be averaged over time ( T ).

(2) Zones with intermittent interruption of supply air: The average outdoor airflow supplied to the breathing zone over time ( T ) shall be not less than the breathing zone outdoor airflow ( Vbz ) calculated using Equation 403.2.1.

(3) Systems with intermittent closure of the outdoor air intake: The average outdoor air intake over time ( T ) shall be not less than the minimum outdoor air intake ( Vot ) calculated using Equation 403.3, Equation 403.4, or Equation 403.5.1 as applicable.

[ASHRAE 62.1:6.2.5.2]

403.7 Exhaust Ventilation. Exhaust airflow shall be provided in accordance with the requirements in Table 403.7. Exhaust makeup air shall be permitted to be a combination of outdoor air, recirculated air, and transfer air.

403.7.1 Parking Garages. Exhaust rate for parking garages shall be in accordance with Table 403.7. Exhaust rate shall not be required for enclosed parking garages having a floor area of 1000 square feet (92.9 m [2] ) or less and used for the storage of 5 or less vehicles.

403.7.2 Enclosed Parking Garages. Mechanical ventilation systems for enclosed parking garages shall operate continuously.

Exceptions:

(1) Mechanical ventilation systems shall be permitted to operate intermittently where the system is designed to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.

(2) Approved automatic carbon monoxide sensing devices, and nitrogen dioxide detectors shall be permitted to modulate the ventilation system to not exceed a maximum average of 50 parts per million of carbon monoxide, or 1 part per million nitrogen dioxide during an eight-hour period with a concentration of not more than 200 parts per million for carbon monoxide, or 5 parts per million nitrogen dioxide, for a period not exceeding 15 minutes. Automatic sens

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VENTILATION AIR

ing devices installed in modulated parking garage ventilation systems shall be approved in accordance with Section 301.2.

403.7.2.1 Alternative Exhaust Ventilation for Enclosed Parking Garages.
CMC § 403.7.1 High relevance — show source text
403.7.1 Parking Garages. Exhaust rate for parking garages shall be in accordance with Table 403.7. Exhaust rate shall not be required for enclosed parking garages having a floor area of 1000 square feet (92.9 m [2] ) or less and used for the storage of 5 or less vehicles.

403.7.2 Enclosed Parking Garages. Mechanical ventilation systems for enclosed parking garages shall operate continuously.

Exceptions:

(1) Mechanical ventilation systems shall be permitted to operate intermittently where the system is designed to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.

(2) Approved automatic carbon monoxide sensing devices, and nitrogen dioxide detectors shall be permitted to modulate the ventilation system to not exceed a maximum average of 50 parts per million of carbon monoxide, or 1 part per million nitrogen dioxide during an eight-hour period with a concentration of not more than 200 parts per million for carbon monoxide, or 5 parts per million nitrogen dioxide, for a period not exceeding 15 minutes. Automatic sens

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VENTILATION AIR

ing devices installed in modulated parking garage ventilation systems shall be approved in accordance with Section 301.2.

403.7.2.1 Alternative Exhaust Ventilation for Enclosed Parking Garages.

403.7.2.2 Minimum Exhaust Rate. [HCD 1 & 2] In lieu of the exhaust rates in Table 403.7, venti- lation systems shall be capable of providing 14,000 cfm (6608 L/s) of exhaust air for each operating vehicle. Number of operating vehicles shall be deter- mined based on 2.5 percent of all parking spaces (and not less than one vehicle).

403.7.2.3 Exhaust Inlet Distribution. [HCD 1 & 2] To ensure proper exhaust of contaminated air and fumes from parking garages, exhaust systems utilizing multiple exhaust inlets shall be designed so that exhaust inlets are distributed in such a manner

that no portion of the parking garage is more than 50 feet (15 240 mm) from an exhaust inlet. Such exhaust inlets shall be installed so that the highest elevation of the exhaust inlet is no greater than 12 inches (305 mm) below the lowest ceiling level.

Exception: Garage exhaust systems designed with- out distributed exhaust inlets may have their exhaust inlets designed based on the principles of engineering and mechanics and shall provide the minimum required exhaust rate in Table 403.7.

403.7.2.4 Exhaust System Operation. [HCD 1 & 2] Exhaust systems shall operate continuously unless one of the exceptions to continuous operation of Section 403.7.2 is utilized.

403.8 Dynamic Reset. The system shall be permitted to be designed to reset the outdoor air intake flow ( Vot ), the space or ventilation zone airflow ( Voz ) as operating conditions change, or both. [ASHRAE 62.1:6.2.6]

403.9 Air Classification and Recirculation. Air shall be
CMC § 0.0929 High relevance — show source text
(1) 60 CFM/person for cultivation, production, and processing facilities or factories.

(2) 15 CFM/person for centers and dispensaries.

Ra = outdoor airflow rate required per unit area, 1 CFM/ft [2]

For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute =

0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per

minute per square foot = 5.08 [(L/s)/m [2] ]

Sample Calculation: Determine the outdoor airflow required in the breathing zone ( Vbz ) of an indoor space used for horticultural cultivation with an occupiable floor area of 800 square feet and a maximum of 5 people expected to occupy the zone.

Sample Solution: Vbz = Rp - Pz + Ra - Az Vbz = (60 CFM/person • 5 people) + (1 CFM • 800 SF) Vbz = 1100 CFM. The ventilation system shall be capable of providing not less than 1100 CFM of outdoor air.

I 801.1.2 Ventilation System Requirements. When activated by the gas detection system required by Section I 601.1, the mechanical purge ventilation system shall remain on until manually reset. The purge ventilation system ducting shall terminate outdoors in an approved location. The ventilation system shall be designed to operate at a negative pressure of 0.01 inches water column (0.002 kPa) in relation to the exhausted indoor space.

I 801.1.3 Ventilation for Indoor Cultivation and Storage Spaces. Indoor spaces used for horticultural cultivation and processing and storage shall be provided with ventilation in accordance with Section 402.2. Where

mechanical ventilation is provided, the systems shall be operational when the indoor space(s) are occupied. Air in indoor cultivation and storage spaces shall be classified as Class 2 Air in accordance with Section 403.9.2.

I 801.1.4 Exhaust Ventilation Rate. The exhaust and ventilation system required in this section shall not create a lesser standard of installation than prescribed by the

minimum safety standards adopted by the Authority Having Jurisdiction. Exhaust airflow shall be provided at not less than 0.2 CFM/ft [2] [1.02 (L/s)/m [2] ] of floor area. Exhaust air shall not be used as makeup air, recirculated air, or transfer air. Makeup air shall be provided for more than 150 CFM (70.8 L/s) exhaust. I 801.1.5 Exhaust System Requirements. An exhaust system shall be installed in accordance with Section 505.0 and the following requirements:

(1) Exhaust outlet location(s) in accordance with Section 502.2.3 for product conveying ducts as classified in Section 505.8.

(2) Exhaust air shall terminate directly to the outdoors and shall not be directed onto a public way.

(3) The exhaust inlet shall be not less than 12 inches (305 mm) above the finished floor.

(4) Chemical fume hoods shall be required for flammable solvent processing, shall be listed, and shall be installed in accordance with the manufacturer’s

installation instructions.

(5) Exhaust ducts shall be independent of all other exhaust systems.

(6) The exhaust rate shall be in accordance with the appliable occupancy category as shown in Table 403.7.
CMC § 503.5.11.3 High relevance — show source text
A + B - ( E/M ) ≥ 50% (Equation E 503.5.11.3)

Where:

A = Percentage that the exhaust and makeup airflow rates are capable of being reduced from design conditions.

B = Sensible energy recovery ratio.

E = Exhaust airflow rate through the heat recovery device at design conditions.

M = Makeup airflow rate of the system at design conditions.

(2) VAV laboratory exhaust and room supply systems that are required to have minimum circulation rates to be in accordance with the codes or

accreditation standards shall be capable of and configured to reduce zone exhaust and makeup airflow rates to the regulated minimum circulation values, or the minimum required to maintain pressurization relationship requirements. Systems serving nonregulated zones shall be capable of and configured to reduce exhaust and makeup airflow rates to 50 percent of the zone design values, or the minimum required to maintain pressurization relationship requirements.

(3) Direct makeup (auxiliary) air supply of 75 percent or more of the exhaust airflow rate, heated not more than 2°F (1°C) below room setpoint, cooled to not less than 3°F (2°C) above room setpoint, no humidification added, and no simultaneous heating and cooling are used for dehumidification control. [ASHRAE 90.1:6.5.7.3]

E 503.5.12 Radiant Heating Systems. Radiant heating systems shall be in accordance with Section E 503.5.12.1 through Section E 503.5.12.2.

E 503.5.12.1 Heating Unenclosed Spaces. Radiant heating shall be used when heating is required for unenclosed spaces.

Exception: Loading docks equipped with air curtains. [ASHRAE 90.1:6.5.8.1]

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APPENDIX E

to permit a determination of compliance by the building official and to indicate compliance with the requirements of this appendix. [ASHRAE 90.1:4.2.2.1] E 503.6.2 Supplemental Information. Supplemental information necessary to verify compliance with this appendix, such as calculations, worksheets, compliance forms, vendor literature, or other data, shall be made available where required by the Authority Having Jurisdiction. [ASHRAE 90.1:4.2.2.2]

E 503.6.3 Manuals. Operating and maintenance information shall be provided to the building owner. This information shall include, but not be limited to, the information specified in Section E 503.6.3.1, Section E 503.6.3.2, and Section E 503.6.5.2. [ASHRAE 90.1:4.2.2.3]

E 503.6.3.1 Required Information. Construction documents shall require that an operating manual and maintenance manual be provided to the building owner. The manuals shall include, at a minimum, the following:

(1) Submittal data stating equipment rating and selected options for each piece of equipment requiring maintenance.

(2) Operation manuals and maintenance manuals for each piece of equipment requiring maintenance. Required routine maintenance actions shall be clearly identified.

(3) Names and addresses of not less than one qualified service agency.
CMC § 90.1 High relevance — show source text
(2) Disable mechanical cooling or reset the cooling setpoint to 90°F (32°C) or more within five minutes of the door opening. Mechanical cooling shall be permitted to remain enabled where outdoor air temperature is less than the space temperature.

Exceptions:

(1) Building entries with automatic closing devices.

(2) Any space without a thermostat.

(3) Alterations to existing buildings.

(4) Loading docks. [ASHRAE 90.1:6.5.10]

E 503.6 Submittals. The Authority Having Jurisdiction shall require submittal of compliance documentation and supplemental information in accordance with Section E 503.6.1 through Section E 503.6.3.

E 503.6.1 Construction Details. Compliance documents shall show all the pertinent data and features of the building, equipment, and systems in sufficient detail

TABLE E 503.5.13

HOT GAS BYPASS LIMITATION

[ASHRAE 90.1: TABLE 6.5.9]

For SI units: 1000 British thermal units per hour = 0.293 kW

»

to be in accordance with Section E 503.5.11.2.2, additional performance testing shall be required to demonstrate proper capture and containment at minimum airflow. [ASHRAE 90.1:6.5.7.2.4]

E 503.5.11.3 Laboratory Exhaust Systems. Buildings with laboratory exhaust systems having a total exhaust rate of more than 5000 ft [3] /min (2.3597 m [3] /s) shall include not less than one of the following features:

(1) VAV laboratory exhaust and room supply systems capable of and configured to reduce exhaust and makeup airflow rates, incorporate a heat recovery system to precondition makeup air from laboratory exhaust, or both, and shall be in accordance with the following:

A + B - ( E/M ) ≥ 50% (Equation E 503.5.11.3)

Where:

A = Percentage that the exhaust and makeup airflow rates are capable of being reduced from design conditions.

B = Sensible energy recovery ratio.

E = Exhaust airflow rate through the heat recovery device at design conditions.

M = Makeup airflow rate of the system at design conditions.

(2) VAV laboratory exhaust and room supply systems that are required to have minimum circulation rates to be in accordance with the codes or

accreditation standards shall be capable of and configured to reduce zone exhaust and makeup airflow rates to the regulated minimum circulation values, or the minimum required to maintain pressurization relationship requirements. Systems serving nonregulated zones shall be capable of and configured to reduce exhaust and makeup airflow rates to 50 percent of the zone design values, or the minimum required to maintain pressurization relationship requirements.

(3) Direct makeup (auxiliary) air supply of 75 percent or more of the exhaust airflow rate, heated not more than 2°F (1°C) below room setpoint, cooled to not less than 3°F (2°C) above room setpoint, no humidification added, and no simultaneous heating and cooling are used for dehumidification control. [ASHRAE 90.1:6.5.7.3]

E 503.5.12 Radiant Heating Systems. Radiant heating systems shall be in accordance with Section E 503.5.12.1 through Section E 503.5.12.2.
CMC § 519.5 High relevance — show source text
519.5, 701.11

Underground. . . . . . . . . . . . . . . . . . . . . . . 510.8, 603.11

– E –

ECONOMIZER, AIR . . . . . . . . . . . . . E 503.5.1, E 503.5.1.2,

Table E 503.5.1.2

ECONOMIZER, WATER . . . . . . . . . . E 503.5.2, E 503.5.2.1,

Table E 503.5.2

ECONOMIZERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407.6

ELECTRIC HEATING APPLIANCES

Air conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.1

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

Duct heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905.9

Room heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.2

ELECTRICAL CODE

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0

ENCLOSED PARKING GARAGES . . . . . . . . . . . . . . 403.7.2

Alternative Exhaust Ventilation. . . . . . . . . . . . . 403.7.2.1

Exhaust Systems Operation. . . . . . . . . . . . . . . 403.7.2.4

Minimum Exhaust Rate . . . . . . . . . . . . . . . . . . 403.7.2.2

ENCLOSURE OF DUCTS,

COMMERCIAL KITCHEN EXHAUST

Clearances . . . . . . . . . . . . . . 507.4.6.3, 507.4.8, 510.7.3

Continuous. . . . . . . . . . . . . . . . . . . . . . . . . 205.0, 510.7

Ducts within . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510.7.8

Fire doors required . . . . . . . . . . . . . . . . . . . . . . . 510.7.7

Grease, factory built . . . . . . . . . . . . . . . . 208.0, 507.4.4,

507.4.6, 507.4.6.3

Grease duct, field-applied. . . . . . . . . . . . 208.0, 507.4.5,

507.4.6, 507.4.6.3
CMC § 403.7.2 High relevance — show source text
ENCLOSED PARKING GARAGES . . . . . . . . . . . . . . 403.7.2

Alternative Exhaust Ventilation. . . . . . . . . . . . . 403.7.2.1

Exhaust Systems Operation. . . . . . . . . . . . . . . 403.7.2.4

Minimum Exhaust Rate . . . . . . . . . . . . . . . . . . 403.7.2.2

ENCLOSURE OF DUCTS,

COMMERCIAL KITCHEN EXHAUST

Clearances . . . . . . . . . . . . . . 507.4.6.3, 507.4.8, 510.7.3

Continuous. . . . . . . . . . . . . . . . . . . . . . . . . 205.0, 510.7

Ducts within . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510.7.8

Fire doors required . . . . . . . . . . . . . . . . . . . . . . . 510.7.7

Grease, factory built . . . . . . . . . . . . . . . . 208.0, 507.4.4,

507.4.6, 507.4.6.3

Grease duct, field-applied. . . . . . . . . . . . 208.0, 507.4.5,

507.4.6, 507.4.6.3

Product conveying ducts . . . . . . . . . . . . . . . . . . . . 505.8

ENCLOSURES

For equipment on roof. . . . . . . . . . . . . . . . . . . . . . 303.8

For boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001.2

ENERGY STAR, DEFINITION . . . . . . . . . . . . . . . . . . E 201.1

ENFORCEMENT (SFM) . . . . . . . . . . . . . . . . . . . . . . . 1.11.2.1

ENFORCING AGENCY

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0

SFM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11.2

ENGINE, GAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1602.0

EQUIPMENT

Clearances. . . . . . . . . 303.10, 303.10.1, Table 303.10.1

Converted equipment . . . . . . . . . . . . . . . . . . . . . . 902.3

578 2025 CALIFORNIA MECHANICAL CODE
CMC § 1.1. Medium relevance — show source text
(1) The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall comply with UL 507.

(2) Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.

(3) Domestic cooking appliances with integral downdraft exhaust equipment shall comply with UL 858 or CSA/ANSI Z21.1/CSA 1.1.

(4) Microwave ovens with integral exhaust for installation over the cooking surface shall comply with UL 923.

(5) All domestic kitchen exhaust ducts used in conjunction with domestic range or cooktop hoods shall be constructed of metal and shall have smooth interior surfaces, fastened and sealed with duct mastic or metal tapes that meet the requirements of UL 181A.

Exception: Ducts for domestic kitchen downdraft grillrange ventilation installed under a concrete slab floor shall be permitted to be of approved Schedule 40 PVC provided the following conditions are met:

(1) The under-floor trench in which the duct is installed shall be completely backfilled with sand or gravel.

(2) Not more than 1 inch (25.4 mm) of 6 inch diameter (150 mm) PVC coupling shall be permitted to protrude above the concrete floor surface.

(3) PVC pipe joints shall be solvent cemented to provide an air and greasetight duct.

(4) The duct shall terminate above grade outside the building and shall be equipped with a backdraft damper.

(6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.

504.4 Clothes Dryers. A clothes dryer exhaust duct shall not be connected to a vent connector, gas vent, chimney, and shall not terminate into a crawl space, attic, or other concealed space. Exhaust ducts shall not be assembled with screws or other fastening means that extend into the duct and that are capable of catching lint, and that reduce the efficiency of the exhaust system. Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed and labeled in accordance

with UL 2158A, or installed in accordance with the clothes dryer manufacturer’s installation instructions. Clothes dryer exhaust ducts shall terminate to the outside of the building in accordance with Section 502.2.1 and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Devices, such as fire or smoke dampers that will obstruct the flow of the exhaust shall not be used. Where joining of ducts, the male end shall be inserted in the direction of airflow.

504.4.1 Provisions for Makeup Air. Makeup air shall be provided in accordance with the following:

(1) Makeup air shall be provided for Type 1 clothes dryers in accordance with the manufacturer’s installa tion instructions. [NFPA 54:10.4.4.1] Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches (0.065 m [2] ) for makeup air shall be provided in the door or by other approved means.
CMC § 712.1.5.2 Medium relevance — show source text
712.1.5.2 Joints in or between nonfire-resistance-rated floor assemblies. Joints in or between floor assemblies without a required fire-resistance rating shall be permitted where they comply with one of the following:
1. The joint shall be concealed within the cavity of a wall.
2. The joint shall be located above a ceiling.
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FIRE AND SMOKE PROTECTION FEATURES
1. The joint shall be sealed, treated or covered with an approved material or system to resist the free passage of flame and the products of combustion.
Exception: Joints meeting one of the exceptions specified in Section 715.3.

712.1.6 Ducts and air transfer openings. Penetrations by ducts and air transfer openings shall be protected in accordance with Section 717. Grease ducts shall be protected in accordance with the California Mechanical Code.

712.1.7 Atriums. Atriums complying with Section 404 that connect two or more stories in Group I-2 or I-3 occupancies or three or more stories in other occupancies shall be permitted.

Exceptions:
1. Atriums shall not be permitted within Group H occupancies.
2. Balconies or stories within Groups A-1, A-4 and A-5 and mezzanines that comply with Section 505 shall not be considered a story as it applies to this section
712.1.8 Masonry chimney. Approved vertical openings for masonry chimneys shall be permitted where the annular space is fireblocked at each floor level in accordance with Section 718.2.5.

712.1.9 Two-story openings. In other than Groups I-2 and I-3, a vertical opening that is not used as one of the applications specified in this section shall be permitted if the opening complies with all of the following items:
1. Does not connect more than two stories.
2. Does not penetrate a horizontal assembly that separates fire areas or smoke barriers that separate smoke compartments.
3. Is not concealed within the construction of a wall or a floor/ceiling assembly.
4. Is not open to a corridor in Group I and R occupancies.
5. Is not open to a corridor on nonsprinklered floors.
6. Is separated from floor openings and air transfer openings serving other floors by construction conforming to required shaft enclosures.
712.1.10 Parking garages. Vertical openings in parking garages for automobile ramps, elevators and duct systems shall comply with Section 712.1.10.1, 712.1.10.2 or 712.1.10.3, as applicable.

712.1.10.1 Automobile ramps. Vertical openings for automobile ramps in parking garages shall be permitted where constructed in accordance with Sections 406.5 and 406.6.

712.1.10.2 Elevators. Vertical openings for elevator hoistways in parking garages that serve only the parking garage, and complying with Sections 406.5 and 406.6, respectively, shall be permitted.

712.1.10.3 Duct systems. Vertical openings for mechanical exhaust or supply duct systems in parking garages complying with Sections 406.5 and 406.6, respectively, shall be permitted to be unenclosed where such duct system is contained within and serves only the parking garage.
CMC § 406.5.7 Medium relevance — show source text
[BE] 406.5.7 Means of egress. Where persons other than parking attendants are permitted, open parking garages shall meet the means of egress requirements of Chapter 10. Where persons other than parking attendants are not permitted, there shall be not fewer than two exit stairways. Each exit stairway shall be not less than 36 inches (914 mm) in width. Lifts shall be permitted to be installed for use of employees only, provided that they are completely enclosed by noncombustible materials.

[F] 406.5.8 Standpipe system. An open parking garage shall be equipped with a standpipe system as required by Section 905.3.

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SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY AND USE

406.5.9 Enclosure of vertical openings. Enclosure shall not be required for vertical openings except as specified in Section 406.5.7.

406.5.10 Ventilation. Ventilation, other than the percentage of openings specified in Section 406.5.2, shall not be required.

406.5.11 Prohibitions. The following uses and alterations are not permitted:
1. Vehicle repair work.
2. Parking of buses, trucks and similar vehicles.
3. Partial or complete closing of required openings in exterior walls by tarpaulins or any other means.
4. Dispensing of fuel.
406.6 Enclosed parking garages. Enclosed parking garages shall comply with Sections 406.2, 406.4 and 406.6.

406.6.1 Heights and areas. Enclosed vehicle parking garages and portions thereof that do not meet the definition of open parking garages shall be limited to the allowable heights and areas specified in Sections 504 and 506 as modified by Section 507. Roof parking is permitted.

406.6.2 Ventilation. A mechanical ventilation system and exhaust system shall be provided in accordance with Chapters 4 and 5 of the California Mechanical Code .

Exception: Mechanical ventilation shall not be required for enclosed parking garages that are accessory to one- and twofamily dwellings.

[F] 406.6.3 Automatic sprinkler system. An enclosed parking garage shall be equipped with an automatic sprinkler system in accordance with Section 903.2.10.

406.6.4 Mechanical-access enclosed parking garages. Mechanical-access enclosed parking garages shall be in accordance with Sections 406.6.4.1 through 406.6.4.4.

406.6.4.1 Separation. Mechanical-access enclosed parking garages shall be separated from other occupancies and accessory uses by not less than 2-hour fire barriers constructed in accordance with Section 707 or by not less than 2-hour horizontal assemblies constructed in accordance with Section 711, or both. Refer to Table 508.4 for additional requirements.

406.6.4.2 Smoke removal. A mechanical smoke removal system, installed in accordance with Section 910.4, shall be provided for all areas containing a mechanical-access enclosed parking garage.
CMC § 507.10 Medium relevance — show source text
507.10 Protection of Gas Appliances from Fumes or Gases other than Products of Combustion. Nondirect-vent appliances installed in beauty shops, barber shops, or other facilities where chemicals that generate corrosive or flammable products such as aerosol sprays are routinely used shall be located in a mechanical room separate or partitioned off from other areas with provisions for combustion and dilution air from outdoors. Direct-vent appliances in such facilities shall be in accordance with the appliance manufacturer’s installation instructions. [NFPA 54:9.1.6.2]

507.11 Process Air. In addition to air needed for combustion in commercial or industrial processes, process air shall be provided as required for cooling of appliances, equipment, or material; for controlling dew point, heating, drying, oxidation, dilution, safety exhaust, odor control, and air for compressors; and for comfort and proper working conditions for personnel. [NFPA 54:9.1.7]

507.12 Flammable Vapors. Appliances shall not be installed in areas where the open use, handling, or dispensing of flammable liquids occurs, unless the design, operation, or installation reduces the potential of ignition of the flammable vapors. Appliances installed in compliance with Section 507.13 through Section 507.15 shall be considered to comply with the intent of this provision. [NFPA 54:9.1.9]

507.13 Installation in Residential Garages. Appliances in residential garages and in adjacent spaces that open to the garage and are not part of the living space of a dwelling unit shall be installed so that all heating elements, switches, burners, and burner-ignition devices are located not less than 18 inches (457 mm) above the floor.

Exception: Listed flammable vapor ignition resistant (FVIR) appliances. {NFPA 54:9.1.10.1 } 507.13.1 Physical Damage. Appliances installed in garages, warehouses, or other areas subject to mechanical damage shall be guarded against such damage by being installed behind protective barriers or by being elevated or located out of the normal path of vehicles.

507.13.2 Access from the Outside. Where appliances are installed in a separate, enclosed space having access only from outside of the garage, such appliances shall be permitted to be installed at floor level, providing the required combustion air is taken from the exterior of the garage. [NFPA 54:9.1.10.3]

507.14 Installation in Commercial Garages. Appliances installed in commercial garages shall comply with Section 507.14.1 and Section 507.14.2.

507.14.1 Parking Structures. Appliances installed in enclosed, basement, and underground parking structures shall be installed in accordance with NFPA 88A. [NFPA 54:9.1.11.1] 507.14.2 Repair Garages. Appliances installed in repair garages shall be installed in accordance with NFPA 30A. [NFPA 54:9.1.11.2] 507.15 Installation in Aircraft Hangars. Heaters in aircraft hangars shall be installed in accordance with NFPA 409.

[NFPA 54:9.1.12] 507.16 Venting of Flue Gases. Appliances shall be vented in accordance with the provisions of Section 509.0. [NFPA 54:9.1.14]

**507.17 Extra Device or Attachment.
CMC § 701.1 Medium relevance — show source text
701.1, 701.1.1, 701.8, 701.10,

802.6.3.1, 902.2, 902.12, 902.13

Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (see Ducts) Economizer . . . . . . . . . . . . . . . . . (see Economizer, air) Exhaust . . . . . . . . . . . . . . . . . . . . . . . (see Air, exhaust) Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . (see Filters, air) Furnace . . . . . . . . . . . . . . . . . (see Furnaces, warm air) Heaters. . . . . . . . . . . . . . . . . . . . . . . . . (see Heater, air)

Makeup . . . . . . . . . . . . . . . 203.0, 401.1, 403.7, 504.4.1,

505.10, 511.3, 517.1.2, 517.1.3,

517.6.1, 517.6.2, 519.6, 701.1,

701.3, 930.5.4, 1106.2.8, 1106.6,

1106.11.11.1, 1220.5, E 503.4.6.9,

E 503.5.11.3, I 801.1.4

Moving Systems . . . . . . . . . . . . . 203.0, 609.1, I 801.1.6, Outside 203.0, Table 310.3,

311.1, 311.3, Chapter 4,

908.3.2, 932.1, 1105.1,

E 502.10.2, E 805.0

Pollution control

devices. . . . . . . . . . . . . . . . . . . 203.0, 512.3, 512.3.5,

513.1.1, 513.3.3

2025 CALIFORNIA MECHANICAL CODE 571

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INDEX

Recirculation. . . . . . . . . . . . . . . . . . 403.3, 403.5, 403.7,

403.9, 404.3, 407.4.5, 512.3.5

Replacement . . . . . . . . . . . . . . . . . . . (see Air, makeup)

Return . . . . . . . . . . . . . 203.0, 311.0, 402.3, 403.2.2.1.2,

403.2.2.2.2, 404.3.2, 517.1.2,

604.4, 905.6, 1105.1, Appendix E

Supply . . . . . . . . . . 203.0, Chapter 4, 914.5, 1104.2.3.2

Frequently asked questions

What exactly does “makeup air” mean here?

Makeup air is the air supplied to replace the air that an exhaust system removes. The CMC allows makeup air to be provided as a combination of outdoor air, recirculated air, and transfer air under § 403.7.

Are small residential garages exempt from ventilation?

An enclosed parking garage used for storage that is 1000 ft² or smaller and stores 5 or fewer vehicles is exempt from the exhaust rate requirement in § 403.7.1. Note: other codes (e.g., energy, fire, local ordinances) may still impose requirements.

Can I use CO sensors to cut fan runtime?

Yes — § 403.7.2 permits intermittent operation if the system uses approved automatic detection or CO/NO2 sensors, provided the sensors and control keep concentrations within the limits in the exceptions.

What if I don’t want to use the 14,000 cfm per operating vehicle alternative?

Then size the system using the exhaust rates contained in Table 403.7 (occupancy‑specific rates). The table itself was not included in the retrieved files, so consult the actual code book or the AHJ for the table values.

Do makeup‑air temperature or conditioning requirements appear here?

Section § 403.7 permits the source of makeup air but does not in the retrieved text set conditioning or temperature limits for makeup air; other sections or the energy code may control how makeup air is treated. Consult the CMC and California Energy Code for conditioning/energy requirements.

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Related in the CMC

Where must outdoor air intakes be located and how far from contaminants?

Primary/secondary airflow, air balance and required primary outdoor‑air fraction

Ventilation system details: intakes, dampers, and filter (MERV) requirements

Outdoor air intakes, makeup air and system details

California Mechanical Code