CMC · California Mechanical Code

Dynamic reset, demand control and controls for minimum outdoor air

Q: What is the single most important control requirement from §§ 403.6 and 403.8?

You may reset outdoor‑air intake and zone airflow as conditions change (dynamic reset, § 403.8 ), but you must still be able to supply the required breathing‑zone minimum ventilation to any occupied zone at full and part load (design and part‑load capability per § 403.6 ).

Q: Does § 403.6 allow me to reduce outdoor air to any lower value at part load?

No — § 403.6 permits reducing the outdoor‑air intake below the design value at part load, but the system must still be capable of providing the minimum breathing‑zone ventilation to occupied zones. You must size VAV minimums and OA controls accordingly.

Q: Where are the DCV (CO2 sensor, setpoint, commissioning) rules located?

DCV device requirements, sensor placement, CO2 setpoints and commissioning procedures are given in CMC Appendix E (see E805.6) and the California Energy Code; §§ 403.6 and 403.8 do not list those device‑level details.

Q: Is a fixed minimum damper position “dynamic control”?

No — fixed minimum damper position alone is not considered a dynamic control strategy. The Energy Code and Appendix guidance require dynamic control methods (and measured OA verification) rather than simply setting a fixed minimum damper position.

Q: What should a plan reviewer check to confirm compliance?

Confirm the design-sized Vot and each zone Vpz‑min (Voz × 1.5 where applicable) are documented, that DDC logic or OA damper modulation is shown for reset, and that Appendix E commissioning forms (e.g., DCV/economizer tests) are included where applicable.

The CMC allows automatic resetting of the outdoor‑air intake and zone airflows to save energy, but your controls must always be able to supply the required minimum ventilation to occupied spaces. Sections §403.6 and §403.8 permit reset strategies but keep the breathing‑zone minimum as the non‑negotiable requirement.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Mechanical Code allows HVAC systems to dynamically reset outdoor-air intake and zone/supply airflows as operating conditions change, but they must still be capable of providing the required minimum ventilation to the breathing zone when spaces are occupied. This permission and the breathing‑zone requirement are stated in § 403.8 and § 403.6 of the CMC respectively. § 403.6 requires systems be designed to meet minimum breathing‑zone ventilation at full- and part‑load conditions; § 403.8 explicitly permits resetting outdoor air intake flow (Vot) and zone/ventilation airflow (Voz) as conditions change.

You may reset outdoor‑air and zone airflow as loads change, but the system must still be capable of supplying the minimum breathing‑zone ventilation to occupied zones (i.e., don’t “save energy” by reducing ventilation below the breathing‑zone minimum while a space is occupied).

Requirements in detail

Key defined terms (first mention bolded)

Dynamic reset — the control strategy that automatically changes outdoor‑air intake and/or zone/supply airflow as operating conditions change. § 403.8.
Minimum outdoor air intake flow (Vot) — the system‑level outside‑air intake rate sized to meet breathing‑zone ventilation requirements (see §§ 403.5, 403.6).
Breathing zone — the region of occupied space for which the minimum ventilation rate is specified; systems must provide required breathing‑zone ventilation when the zone is occupied. § 403.6.
Part‑load conditions — operating points below equipment design capacity; the Code allows reducing the outdoor‑air intake at part load provided breathing‑zone needs are still met. § 403.6.

What the two controlling sections say (plain summary)

§ 403.6 — Ventilation systems must be designed to provide at least the minimum breathing‑zone ventilation where zones are occupied for all full‑ and part‑load conditions; the minimum outdoor‑air intake flow may be less than the design value at part load.
§ 403.8 — Systems are permitted to be designed to reset outdoor‑air intake flow (Vot), the space or ventilation zone airflow (Voz), or both, as operating conditions change.

Decision‑relevant dimensions — what to check when you design or review controls

Decision / dimension	Typical values / rule of thumb	Why it matters	Code reference
Must the system be able to meet breathing‑zone min when occupied?	Yes — at full and part load	Prevents under‑ventilation during occupancy	§ 403.6
Is it allowed to reduce Vot at part load?	Yes — the Code permits Vot < design at part load provided breathing‑zone min is met	Saves energy while maintaining IAQ	§ 403.6
Can both Vot and Voz be reset?	Yes — either or both may be reset automatically	Flexibility in control strategies (e.g., VAV resets, OA damper)	§ 403.8
Minimum primary zone airflow to allow outdoor‑air fraction	Vpz‑min = Voz × 1.5 (design; established in § 403.5.1.4)	Ensures a VAV box can deliver enough primary air to meet breathing‑zone OA	§ 403.5.1.4 and § 403.6
Verification / commissioning	Functional tests for DCV and economizers are specified in Appendix E (e.g., E805.6 for DCV)	Ensures controls actually achieve dynamic reset and minimum OA	CMC Appendix E (E805.6)

How designers typically implement dynamic reset in practice

Use VAV box minimums sized so the zone primary airflow at minimum still allows the outdoor‑air fraction to meet breathing‑zone requirements (see § 403.5.1.4).
Implement OA damper modulation tied to system supply‑fan speed or to VAV signals so that outdoor air delivered is proportional to delivered primary air; support with DDC so alarms and overrides prevent under‑ventilation. § 403.8 permits the resets; Appendix E and the Energy Code supply test and DCV specifics.

Exceptions & special cases

The Code text of § 403.6 allows the minimum outdoor‑air intake flow to be less than design at part load — but this is not a blanket permission to starve occupied spaces of required breathing‑zone ventilation. The breathing‑zone minimum remains the controlling requirement.
The CMC Chapter 4 text (the sections you asked to control — § 403.6 and § 403.8) does not itself spell out CO2 setpoints, sensor locations, commissioning procedures or OA damper maximum/minimum positions for demand‑controlled ventilation. Those test/acceptance and DCV specifics appear in CMC Appendix E and in the California Energy Code; see Appendix E (E805.6) for DCV acceptance testing and criteria.
Systems with VAV control must follow minimum primary airflow sizing rules (e.g., Vpz‑min = Voz × 1.5) so resetting does not make it impossible to meet breathing‑zone OA. § 403.5.1.4 is the reference for that requirement.

If you need a rule not contained in § 403.6 or § 403.8 (for example exact CO2 setpoint limits, required sensor accuracy, or commissioning forms), those are located in Appendix E and the California Energy Code — the CMC sections you specified are permissive for reset but do not list those device/acceptance details.

Common mistakes

Assuming you can reduce outdoor air to zero whenever the system is at part load — the system must still provide required breathing‑zone ventilation to occupied zones (mistake: ignoring § 403.6).
Setting VAV box minimums too low so there is no way to supply the breathing‑zone outdoor‑air requirement when the box is at min airflow (fix: size Vpz‑min per § 403.5.1.4).
Treating a fixed minimum damper position as a “dynamic control” strategy — Energy Code language (and Appendix E guidance) treats fixed minimum positions as non‑dynamic; measured OA must be maintained near the minimum with dynamic control. (See related test/acceptance in Appendix E and Energy Code requirements for dynamic OA control.)
Forgetting to include alarms or BMS logic to detect zones that “drive” the reset algorithm to unacceptable values — good DDC must allow operator removal of problematic zones from reset logic. Appendix E and ASHRAE‑derived DDC guidance cover this.

Worked example — conference room on a VAV system

Scenario: a multi‑zone VAV system serves a conference room with design breathing‑zone outdoor‑air requirement (Voz) = 150 cfm (e.g., 15 cfm/person for 10 people). The designer uses the simplified procedure from § 403.5.

Determine zone minimum primary airflow (to ensure VAV box can supply OA):
Vpz‑min = Voz × 1.5 = 150 cfm × 1.5 = 225 cfm (per § 403.5.1.4). This is the minimum zone primary airflow the system must be able to supply at the design condition so that the outdoor‑air fraction at that primary flow can meet the breathing‑zone Voz.
Apply dynamic reset at part load (allowed by § 403.8):
- Suppose overall system supply airflow is reset down during off‑peak to 70% of design. The VAV box can reduce delivered airflow, but the box minimum must not go below 225 cfm for that conference room if the space remains occupied. That ensures the outdoor‑air fraction available to the room can still meet the 150 cfm breathing‑zone requirement. If the VAV box minimum were set to 120 cfm, then even with a 100% OA fraction the room would receive only 120 cfm OA — below the required 150 cfm, which violates § 403.6.
Demand control (DCV) interplay:
- If DCV is used (e.g., CO2 control) to reduce OA when the room is less than design occupancy, Appendix E prescribes sensor location, setpoint limits and acceptance tests (see E805.6). The CMC permit to reset OA (§ 403.8) does not remove the need to meet DCV and OA verification tests in Appendix E or the Energy Code.

Takeaway: dynamic reset can save energy, but minimum zone primary airflow and breathing‑zone OA requirements set lower limits that controls and minimums must respect.

Related provisions (CMC) — quick references

§ 403.5 — Multiple‑zone recirculating systems and outdoor‑air intake calculations (system ventilation efficiency and zone minimum primary airflow).
§ 403.9 — Air classification and recirculation limits (recirculation restrictions that affect whether you can recirculate air between zones).
Appendix E, E805.6 — Demand‑controlled ventilation acceptance tests and DCV acceptance criteria (sensor location, CO2 setpoints, OA damper response). Note: Appendix E is part of the CMC and supplies test/acceptance detail not spelled out in §§ 403.6/403.8.
Appendix E, E805.5 — Air economizer functional testing (relevant when OA control interacts with economizers).

Code references

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

CMC § 805.6 High relevance — show source text
(6) Where the economizer is disabled, the outdoor air damper closes to a minimum position; the return damper modulates 100 percent open, and mechanical cooling remains enabled. E 805.6 Demand-Controlled Ventilation Systems Acceptance (Form MECH-6A). The purpose of this test is to verify that systems required to employ demand-controlled ventilation shall be permitted to vary outside ventilation flow rates based on maintaining interior carbon dioxide (CO 2 ) concentration setpoints. Demand-controlled ventilation refers to an HVAC system’s ability to reduce outdoor air ventilation flow below design values where the space served is at less than design occupancy. Carbon dioxide is a good indicator of occupancy load and is the basis used for modulating ventilation flow rates.

E 805.6.1 Test Procedure. The procedure for performing a functional test for demand-control ventilation (DVC) systems shall be in accordance with Section E 805.6.1.1 and Section E 805.6.1.2.

E 805.6.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

(1) Carbon dioxide control sensor is factory calibrated or field-calibrated in accordance with this appendix.

(2) The sensor is located in the high-density space between 3 feet (914 mm) and 6 feet (1829 mm) above the floor or at the anticipated level of the occupants’ heads.

(3) DCV control setpoint is at or below the carbon dioxide concentration permitted by this appendix.

E 805.6.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

Step 1: Disable economizer controls.

Step 2: Simulate a signal at or slightly above the carbon dioxide concentration setpoint required by this appendix. Verify and document the following:

(1) For single zone units, outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

(2) For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation requirements.

Step 3: Simulate signal well below the carbon dioxide setpoint. Verify and document the following:

(1) For single zone units, outdoor air damper modulates to the design minimum value.

(2) For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation requirements.

Step 4: Restore economizer controls and remove system overrides initiated during the test.

Step 5: With controls restored, apply carbon dioxide calibration gas at a concentration slightly above the setpoint to the sensor. Verify that the outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

E 805.6.2 Acceptance Criteria. Demand-controlled ventilation systems acceptance criteria shall be as follows:

(1) Each carbon dioxide sensor is factory calibrated (with calibration certificate) or field calibrated.

(2) Each carbon dioxide sensor is wired correctly to the controls to ensure proper control of the outdoor air damper.

(3) Each carbon dioxide sensor is located correctly within the space 1 foot (305 mm) to 6 feet (1829 mm) above the floor.

(4) Interior carbon dioxide concentration setpoint is not more than 600 parts per million (ppm) plus outdoor air carbon dioxide value where dynamically measured or not more than 1000 ppm where no OSA sensor is provided.
CMC § 805.6.2 High relevance — show source text
Step 2: Simulate a signal at or slightly above the carbon dioxide concentration setpoint required by this appendix. Verify and document the following:

(1) For single zone units, outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

(2) For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation requirements.

Step 3: Simulate signal well below the carbon dioxide setpoint. Verify and document the following:

(1) For single zone units, outdoor air damper modulates to the design minimum value.

(2) For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation requirements.

Step 4: Restore economizer controls and remove system overrides initiated during the test.

Step 5: With controls restored, apply carbon dioxide calibration gas at a concentration slightly above the setpoint to the sensor. Verify that the outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

E 805.6.2 Acceptance Criteria. Demand-controlled ventilation systems acceptance criteria shall be as follows:

(1) Each carbon dioxide sensor is factory calibrated (with calibration certificate) or field calibrated.

(2) Each carbon dioxide sensor is wired correctly to the controls to ensure proper control of the outdoor air damper.

(3) Each carbon dioxide sensor is located correctly within the space 1 foot (305 mm) to 6 feet (1829 mm) above the floor.

(4) Interior carbon dioxide concentration setpoint is not more than 600 parts per million (ppm) plus outdoor air carbon dioxide value where dynamically measured or not more than 1000 ppm where no OSA sensor is provided.

(5) A minimum OSA setting is provided where the system is in occupied mode in accordance with this appendix regardless of space carbon dioxide readings.

(6) A maximum OSA damper position for DCV control shall be established in accordance with this appendix, regardless of space carbon dioxide readings.

(7) The outdoor air damper shall modulate open where the carbon dioxide concentration within the space exceeds setpoint.

(8) The outdoor air damper modulates closed (toward minimum position) where the carbon dioxide concentration within the space is below setpoint.

E 805.7 Supply Fan Variable Flow Controls (Form MECH-7A). The purpose of this test is to ensure that the supply fan in a variable air volume application modulates to meet system airflow demand. In most applications, the individual VAV boxes serving each space will modulate the amount of

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APPENDIX E

air delivered to the space based on heating and cooling requirements. As a result, the total supply airflow provided by the central air handling unit shall vary to maintain sufficient airflow through each VAV box. Airflow shall be controlled using a variable frequency drive (VFD) to modulate supply fan speed and vary system airflow. The most common strategy for controlling the VFD is to measure and maintain static pressure within the duct.

E 805.7.1 Test Procedure. The procedure for performing a functional test for supply fan variable controls shall be in accordance with Section E 805.7.1.1 and Sec tion E 805.7.1.2.
CMC § 90.1 High relevance — show source text
(1) Monitor zone damper positions or other indicator of need for static pressure.

(2) Automatically detect those zones that are capable of excessively driving the reset logic and generate an alarm to the system operator.

(3) Readily allow operator removal of zones from the reset algorithm. [ASHRAE 90.1:6.5.3.2.3]

E 503.5.6.2.3 Return and Relief Fan Con-

trol. Return and relief fans used to meet Section E 503.5.1.4 shall comply with all of the following:

(1) Relief air rate shall be controlled to maintain building pressure either directly, or indirectly through differential supplyreturn airflow tracking. Systems with constant speed or multispeed supply fans shall also be allowed to control the relief system based on outdoor air damper position.

(2) Fans shall have variable-speed control or other devices that will result in total return/relief fan system demand of no more than 30 percent of total design power at 50 percent of total design fan flow.

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APPENDIX E

Exceptions:

(1) Return or relief fans with total motor size less than or equal to 0.5 hp (0.37 kW).

(2) Staged relief fans with a minimum of four stages. [ASHRAE 90.1:6.5.3.2.4]

E 503.5.6.3 Multiple-Zone VAV System Venti- lation Optimization Control. Multiple-zone VAV systems with DDC of individual zone boxes reporting to a central control panel shall include means to automatically reduce outdoor air intake flow below design rates in response to changes in system ventilation efficiency in accordance with Section 404.0 or ASHRAE 62.1.

Exceptions:

(1) VAV systems with zonal transfer fans that recirculate air from other zones without directly mixing it with outdoor air, dual-duct dual-fan VAV systems, and VAV systems with fanpowered terminal units.

(2) Systems where total design exhaust airflow is more than 70 percent of total design outdoor air intake flow requirements. [ASHRAE 90.1:6.5.3.3]

E 503.5.6.4 Supply Air Temperature Reset Controls. Multiple zone HVAC systems shall include controls that are capable of and configured to automatically reset the supply air temperature in response to representative building loads, or to outdoor air temperature. The controls shall reset the supply air temperature to at least 25 percent of the difference between the design supply air temperature and the design room air temperature. Controls that adjust the reset based on zone humidity shall be permitted in Climate Zones 0B, 1B, 2B, 3B, 3C, and 4 through 8. HVAC zone that are expected to experience relatively constant loads shall have maximum airflow designed to accommodate the fully reset supply air temperature.

HVAC zones that are expected to experience relatively constant loads typically include electronic equipment rooms and interior zones.

Exceptions:

(1) Systems in Climate Zones 0A, 1A, and 3A with less than 3000 cubic feet per minute (1.4 m [3] /s) of design outdoor air.
CMC § 805.5.2 High relevance — show source text
Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:

(1) Economizer damper shall close to its minimum position.

(2) Applicable fans and dampers shall operate as intended to maintain building pressure.

(3) The unit heating is disabled.

Step 4: Simulate a heating demand, and set the economizer so that it is capable of operating (e.g., actual outdoor air conditions are below lockout setpoint). Verify the economizer is at minimum position.

Step 5: Restore demand control ventilation systems (where applicable) and remove system overrides initiated during the test.

E 805.5.2 Acceptance Criteria. Air economizer controls acceptance criteria shall be as follows:

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APPENDIX E

(1) Where the economizer is factory installed and certified, a valid factory certificate is required for acceptance. No additional equipment tests are necessary.

(2) Air economizer lockout setpoint is in accordance with this appendix. Outside sensor location accurately reads true outdoor air temperature and is not affected by exhaust air or other heat sources.

(3) Sensors are located to achieve the desired control.

(4) During economizer mode, the outdoor air damper shall modulate open to a maximum position and return air damper to 100 percent closed.

(5) The outdoor air damper is 100 percent open before mechanical cooling is enabled and for units 75 000 Btu/h (22 kw) and larger remains at 100 percent open while mechanical cooling is enabled (economizer integration where used for compliance).

(6) Where the economizer is disabled, the outdoor air damper closes to a minimum position; the return damper modulates 100 percent open, and mechanical cooling remains enabled. E 805.6 Demand-Controlled Ventilation Systems Acceptance (Form MECH-6A). The purpose of this test is to verify that systems required to employ demand-controlled ventilation shall be permitted to vary outside ventilation flow rates based on maintaining interior carbon dioxide (CO 2 ) concentration setpoints. Demand-controlled ventilation refers to an HVAC system’s ability to reduce outdoor air ventilation flow below design values where the space served is at less than design occupancy. Carbon dioxide is a good indicator of occupancy load and is the basis used for modulating ventilation flow rates.

E 805.6.1 Test Procedure. The procedure for performing a functional test for demand-control ventilation (DVC) systems shall be in accordance with Section E 805.6.1.1 and Section E 805.6.1.2.

E 805.6.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

(1) Carbon dioxide control sensor is factory calibrated or field-calibrated in accordance with this appendix.

(2) The sensor is located in the high-density space between 3 feet (914 mm) and 6 feet (1829 mm) above the floor or at the anticipated level of the occupants’ heads.

(3) DCV control setpoint is at or below the carbon dioxide concentration permitted by this appendix.

E 805.6.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

Step 1: Disable economizer controls.
CMC § 120.1 High relevance — show source text
iii. When a single zone serves multiple spaces, there shall be an occupant sensor in each space and the zone shall not be considered vacant until all spaces in the zone are vacant. iv. One hour prior to normal scheduled occupancy, the occupant sensor ventilation control shall allow preoccupancy purge as described in Section 120.1(d)2. v. When the zone is scheduled to be occupied and occupant sensing controls in all spaces served by the zone indicate the spaces are unoccupied, the zone shall be placed in occupied-standby mode. vi. In 5 minutes or less after entering occupied-standby mode, mechanical ventilation to the zone shall be shut off until the space becomes occupied or until ventilation is needed to provide space heating or conditioning. When mechanical ventilation is shut off to the zone, the ventilation system serving the zone shall reduce the system outside air rate by the amount of outside air required for the zone. vii. Where the system providing space conditioning also provides ventilation to the zone, in 5 minutes or less after entering occupied-standby mode, space-conditioning zone setpoints shall be reset in accordance with Section 120.2(e)3.

(e) Ducting for zonal heating and cooling units. Where a return plenum is used to distribute outdoor air to a zonal heating or cooling unit, which then supplies the air to a space in order to meet the requirements of Section 120.1(c)3, the outdoor air shall be ducted to discharge either:
1. Within 5 feet of the unit; or
2. Within 15 feet of the unit, substantially toward the unit, and at a velocity not less than 500 feet per minute.
(f) Design and control requirements for quantities of outdoor air.
1. All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls that allow design minimum outside air rates to be operated at no less than the larger of (1) the minimum levels specified in Section 120.1(c)3; or (2) the rate required for make-up of exhaust systems that are required for a covered or noncovered process, for control of odors, or for the removal of contaminants within the space.
2. All variable air volume mechanical ventilation and space-conditioning systems shall include dynamic controls that are capable of maintaining measured outside air ventilation rates within 10 percent of the design minimum outside air ventilation rate at both full and reduced supply airflow conditions. Fixed minimum damper position is not considered to be dynamic and is not an allowed control strategy.
3. All mechanical ventilation and space-conditioning systems shall be tested to confirm their ability to operate within 10 percent of the design minimum outside air rate.
(g) Air classification and recirculation limitations. Air classification and recirculation limitations of air shall be based on the air classification as listed in Table 120.1-A or Table 120.1-C, and in accordance with the requirements of Sections 120.1(g)1 through 4.

Note: Air class definitions are taken directly from ASHRAE 62.1 and are duplicated here for convenience.
1. Class 1 Air is air with low contaminant concentration, low sensory-irritation intensity or inoffensive odor. Recirculation or transfer of Class 1 air to any space shall be permitted; [ASHRAE 62.1:5.13.3.1]
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CMC § 160.2 High relevance — show source text
7. Design and control requirements for quantities of outdoor air . A. All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls to allow outside air rates to be operated at the minimum levels specified in Section 160.2(c)3 or the rate required for make-up of exhaust systems that are required for an exempt or covered process, for control of odors or for the removal of contaminants within the space. B. All variable air volume mechanical ventilation and space-conditioning systems shall include dynamic controls that maintain measured outside air ventilation rates within 10 percent of the required outside air ventilation rate at both full and reduced supply airflow conditions. Fixed minimum damper position is not considered to be dynamic and is not an allowed control strategy. C. Measured outdoor air rates of constant volume mechanical ventilation and space-conditioning systems shall be within 10 percent of the required outside air rate.

8. Air classification and recirculation limitations. Air classification and recirculation limitations of air shall be based on the air classification as listed in Table 160.2-B or Table 160.2-D, in accordance with the following: A. Class 1 air is air with low contaminant concentration, low sensory-irritation intensity or inoffensive odor. Recirculation or transfer of Class 1 air to any space shall be permitted; [ASHRAE 62.1:5.13.3.1] B. Class 2 air is air with moderate contaminant concentration, mild sensory-irritation intensity or mildly offensive odor (Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes). Recirculation or transfer of Class 2 air shall be permitted in accordance with Sections 160.2(c)8Bi through 160.2(c)8Bv: i. Recirculation of Class 2 air within the space of origin shall be permitted [ASHRAE 62.1:5.13.3.2.1]. ii. Recirculation or transfer of Class 2 air to other Class 2 or Class 3 spaces shall be permitted, provided that the other spaces are used for the same or similar purpose or task and involve the same or similar pollutant sources as the Class 2 space [ASHRAE 62.1:5.13.3.2.2]; or iii. Transfer of Class 2 air to toilet rooms [ASHRAE 62.1:5.13.3.2.3]; or

iv. Recirculation or transfer of Class 2 air to Class 4 spaces [ASHRAE 62.1:5.13.3.2.4]. v. Class 2 air shall not be recirculated or transferred to Class 1 spaces. [ASHRAE 62.1:5.13.3.2.5]. Exception to Section 160.2(c)8Bv: When using any energy recovery device, recirculation from leakage, carryover or transfer from the exhaust side of the energy recovery device is permitted. Recirculated Class 2 air shall not exceed 10 percent of the outdoor air intake flow. C. Class 3 air is air with significant contaminant concentration, significant sensory-irritation intensity or offensive odor. Recirculation or transfer of Class 3 air shall be permitted in accordance with Sections 160.2(c)8Ci and 160.2(c)8Cii: i. Recirculation of Class 3 air within the space of origin shall be permitted.
CMC § 805.5.1.1 High relevance — show source text
E 805.5.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

(1) Economizer lockout setpoint is in accordance with this appendix.

(2) Economizer lockout control sensor is located to prevent false readings.

(3) System is designed to provide up to 100 percent outside air without over-pressurizing the building.

(4) For systems with DDC controls lockout sensor(s) are either factory calibrated or field calibrated.

(5) For systems with non-DDC controls, manufacturer’s startup and testing procedures are applied.

E 805.5.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

Step 1: Disable demand control ventilation systems (where applicable).

Step 2: Enable the economizer, and simulate a cooling demand large enough to drive the economizer fully open. Verify and document the following:

(1) Economizer damper is 100 percent opened and return air damper is 100 percent closed.

(2) Where applicable, verify that the economizer remains 100 percent open where the cooling demand can no longer be met by the economizer alone.

(3) Applicable fans and dampers operate as intended to maintain building pressure.

(4) The unit heating is disabled.

Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:

(1) Economizer damper shall close to its minimum position.

(2) Applicable fans and dampers shall operate as intended to maintain building pressure.

(3) The unit heating is disabled.

Step 4: Simulate a heating demand, and set the economizer so that it is capable of operating (e.g., actual outdoor air conditions are below lockout setpoint). Verify the economizer is at minimum position.

Step 5: Restore demand control ventilation systems (where applicable) and remove system overrides initiated during the test.

E 805.5.2 Acceptance Criteria. Air economizer controls acceptance criteria shall be as follows:

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APPENDIX E

(1) Where the economizer is factory installed and certified, a valid factory certificate is required for acceptance. No additional equipment tests are necessary.

(2) Air economizer lockout setpoint is in accordance with this appendix. Outside sensor location accurately reads true outdoor air temperature and is not affected by exhaust air or other heat sources.

(3) Sensors are located to achieve the desired control.

(4) During economizer mode, the outdoor air damper shall modulate open to a maximum position and return air damper to 100 percent closed.

(5) The outdoor air damper is 100 percent open before mechanical cooling is enabled and for units 75 000 Btu/h (22 kw) and larger remains at 100 percent open while mechanical cooling is enabled (economizer integration where used for compliance).
CMC § 160.2 High relevance — show source text
c. When a single zone damper or a single zone system serves multiple spaces, there shall be an occupant sensor in each space and the zone shall not be considered vacant until all spaces in the zone are vacant. d. One hour prior to normal scheduled occupancy, the occupant sensor ventilation control shall allow preoccupancy purge as described in Section 160.2(c)5B. e. When the zone is scheduled to be occupied and occupant sensing controls in all spaces served by the zone indicate the spaces are unoccupied, the zone shall be placed in occupied-standby mode. f. In 5 minutes or less after entering occupied-standby mode, mechanical ventilation to the zone shall be shut off until the space becomes occupied or until ventilation is needed to provide space heating or conditioning. When mechanical ventilation is shut off to the zone, the ventilation system serving the zone shall reduce the system outside air rate by the amount of outside air required for the zone. g. Where the system providing space conditioning also provides ventilation to the zone, in 5 minutes or less after entering occupied-standby mode, space-conditioning zone setpoints shall be reset in accordance with Section 120.2(e)3. 6. Ducting for zonal heating and cooling units. Where a return plenum is used to distribute outdoor air to a zonal heating or cooling unit that then supplies the air to a space in order to meet the requirements of Section 160.2(c)3, the outdoor air shall be ducted to discharge either: A. Within 5 feet of the unit; or

B. Within 15 feet of the unit, substantially toward the unit and at a velocity not less than 500 feet per minute. 7. Design and control requirements for quantities of outdoor air . A. All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls to allow outside air rates to be operated at the minimum levels specified in Section 160.2(c)3 or the rate required for make-up of exhaust systems that are required for an exempt or covered process, for control of odors or for the removal of contaminants within the space. B. All variable air volume mechanical ventilation and space-conditioning systems shall include dynamic controls that maintain measured outside air ventilation rates within 10 percent of the required outside air ventilation rate at both full and reduced supply airflow conditions. Fixed minimum damper position is not considered to be dynamic and is not an allowed control strategy. C. Measured outdoor air rates of constant volume mechanical ventilation and space-conditioning systems shall be within 10 percent of the required outside air rate.

8. Air classification and recirculation limitations. Air classification and recirculation limitations of air shall be based on the air classification as listed in Table 160.2-B or Table 160.2-D, in accordance with the following: A. Class 1 air is air with low contaminant concentration, low sensory-irritation intensity or inoffensive odor. Recirculation or transfer of Class 1 air to any space shall be permitted; [ASHRAE 62.1:5.13.3.1] B. Class 2 air is air with moderate contaminant concentration, mild sensory-irritation intensity or mildly offensive odor (Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes).
CMC § 503.3. High relevance — show source text
Exception : DDC is not required for systems using the simplified approach to compliance in accordance with Section E 503.3. [ASHRAE 90.1:6.4.3.10.1]

E 503.4.6.12.2 DDC Controls. Where DDC is required by Section E 503.4.6.12.1, the DDC

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APPENDIX E

system shall be capable of and configured with all of the following, as required, to provide the control logic required in Section E 503.5:

(1) Monitoring zone and system demand for fan pressure, pump pressure, heating, and cooling.

(2) Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers.

(3) Automatically detecting those zones and systems that are capable of excessively driving the reset logic and generate an alarm or other indication to the system operator.

(4) Readily allowing operator removal of zone(s) from the reset algorithm. [ASHRAE 90.1:6.4.3.10.2]

E 503.4.6.12.3 DDC Display. Where DDC is required in accordance with Section E 503.4.6.12.1 for new buildings, the DDC system shall be capable of trending and graphically displaying input and output points. [ASHRAE 90.1:6.4.3.10.3]

E 503.4.6.13 Economizer Fault Detection and Diagnostics (FDD). Air-cooled direct-expansion cooling units listed in Tables E 503.7.1(1) and E 503.7.1(2), where an air economizer is installed in accordance with Section E 503.5, shall include a fault detection and diagnostics (FDD) system complying with the following:

(1) The following temperature sensors shall be permanently installed to monitor system operation:

(a) Outdoor air

(b) Supply air

(c) Return air, where required for economizer control

(2) The system shall have the capability of displaying the value of each sensor.

(3) The FDD system or unit controls shall be capable of and configured to provide system status by indicating the following:

(a) Free cooling available

(b) Economizer enabled

(c) Compressor enabled

(d) Heating enabled

(e) Mixed-air low-limit cycle active

(4) The FDD system or unit controls shall have provisions to manually initiate each operating mode so that the operation of compressors, economizers, fans, and the heating system can be independently tested and verified.

(5) The FDD system shall be capable of and configured to detect the following faults:

(a) Air temperature sensor failure/fault

(b) Not economizing when the unit should be economizing

(c) Economizing when the unit should not be economizing

(d) Damper not modulating

(e) Excess outdoor air

(6) The FDD system shall be capable of and configured to report faults to a fault management appli

TABLE E 503.4.6.12.1

DDC APPLICATIONS AND QUALIFICATIONS

[ASHRAE 90.1:6.4.3.10.1]

CMC § 503.5.6.5 High relevance — show source text

covered by Section E 503.5.6.5 and having a fan nameplate electrical input power of less than 180 W or having a motor nameplate horsepower less than

1 / 12 hp (62.1 W) shall meet the fan efficacy requirements specified in ASHRAE 90.1. [ASHRAE 90.1:6.5.3.7]

E 503.5.6.7 Ventilation Design. The required minimum outdoor air rate is the larger of the minimum outdoor air rate or the minimum exhaust air rate

required by Chapter 4, ASHRAE 62.1, ASHRAE 62.2, ASHRAE/ASHE 170, or applicable codes or accreditation standards. Outdoor air ventilation systems shall comply with one of the following:

(1) Design minimum system outdoor air provided shall not exceed 135 percent of the required minimum outdoor air rate.

(2) Dampers, ductwork, and controls shall be provided that allow the system to supply no more than the required minimum outdoor air rate with a single setpoint adjustment.

(3) The system includes exhaust air energy recovery complying with Section E 503.5.10.1.

[ASHRAE 90.1:6.5.3.8]

E 503.5.6.8 Occupied-Standby Controls. Zones serving only rooms that are required to have automatic partial OFF or automatic full OFF lighting controls in accordance with ASHRAE 90.1, where the Chapter 4 or ASHRAE 62.1 occupancy category permits ventilation air to be reduced to zero when

438 2025 CALIFORNIA MECHANICAL CODE

APPENDIX E

TABLE E 503.5.6.5(1) MINIMUM AVERAGE FULL-LOAD EFFICIENCY FOR POLYPHASE SMALL ELECTRIC MOTORS* [ASHRAE 90.1: TABLE 10.8-3]	Col2	Col3	Col4
FULL-LOAD EFFICIENCY, %	FULL-LOAD EFFICIENCY, %	FULL-LOAD EFFICIENCY, %	FULL-LOAD EFFICIENCY, %
NUMBER OF POLES	OPEN MOTORS	OPEN MOTORS	OPEN MOTORS
NUMBER OF POLES	2	4	6
SYNCHRONOUS SPEED (rpm)	3600	1800	1200
MOTOR SIZE (hp)	EFFICIENCY, %	EFFICIENCY, %	EFFICIENCY, %
0.25	65.6	69.5	67.5
0.33	69.5	73.4	71.4
0.50	73.4	78.2	75.3
0.75	76.8	81.1	81.7
1	77.0	83.5	82.5
1.5	84.0	86.5	83.8
2	85.5	86.5	N/A
3	85.5	86.9	N/A

For SI units: 1 horsepower = 0.746 kW

CMC § 90.1 High relevance — show source text
[ASHRAE 90.1:6.5.3.2.1]

TABLE E 503.5.6.2

FAN AIRFLOW CONTROL

[ASHRAE 90.1: TABLE 6.5.3.2.1]

COOLING SYSTEM TYPE FAN MOTOR SIZE,
(hp) MECHANICAL
COOLING CAPACITY,
(Btu/h)

DX cooling Any ≥65 000

Chilled-water and evapo-
rative cooling
≥1⁄4
Any

For SI units: 1000 British thermal units per hour = 0.293 kW, 1 horsepower = 0.746 kW, 1 cubic foot per minute = 0.00047 m [3] /s

E 503.5.6.2.1 VAV Static Pressure Sensor Location. Static pressure sensors used to control VAV fans shall be located such that the controller setpoint is not more than 1.2 inches water column (0.30 kPa). Where this results in the sensor being located downstream of major duct splits, sensors shall be installed in each major branch to ensure that static pressure is maintained in each.

Exception: Systems that are in accordance with Section E 503.5.6.2.2. [ASHRAE 90.1:6.5.3.2.2]

E 503.5.6.2.2 VAV Setpoint Reset. For multiple-zone VAV systems having a total fan system motor nameplate horsepower exceeding 5 hp (3.7 kW) with DDC of individual zones reporting to the central control panel, static pressure setpoint shall be reset based on the zone requiring the most pressure, such as the setpoint is reset lower until one zone damper is nearly wide open. Controls shall provide the following:

(1) Monitor zone damper positions or other indicator of need for static pressure.

(2) Automatically detect those zones that are capable of excessively driving the reset logic and generate an alarm to the system operator.

(3) Readily allow operator removal of zones from the reset algorithm. [ASHRAE 90.1:6.5.3.2.3]

E 503.5.6.2.3 Return and Relief Fan Con-

trol. Return and relief fans used to meet Section E 503.5.1.4 shall comply with all of the following:

(1) Relief air rate shall be controlled to maintain building pressure either directly, or indirectly through differential supplyreturn airflow tracking. Systems with constant speed or multispeed supply fans shall also be allowed to control the relief system based on outdoor air damper position.

(2) Fans shall have variable-speed control or other devices that will result in total return/relief fan system demand of no more than 30 percent of total design power at 50 percent of total design fan flow.

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APPENDIX E

Exceptions:

(1) Return or relief fans with total motor size less than or equal to 0.5 hp (0.37 kW).
CMC § 303.10.1 High relevance — show source text
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TABLE OF CONTENTS

323.0 Mechanical Equipment

Schedules . . . . . . . . . . . . . . . . . . . 62

324.0 Diesel-Powered Emergency

Generators . . . . . . . . . . . . . . . . . . . 62

325.0 Alternate Source of Power for

Safe Temperatures. . . . . . . . . . . . . 62

Table 303.10.1 Reduction of Clearances with

Specified Forms of Protection . . . . 63

Table 313.3 Hangers and Supports . . . . . . . . . . 65

CHAPTER 4 VENTILATION AIR . . . . . . . . . . . . 67

401.0 General. . . . . . . . . . . . . . . . . . . . . . 69

401.1 Applicability. . . . . . . . . . . . . . . . . . . 69

401.2 Indoor Swimming Pools . . . . . . . . . 69

401.3 Filters . . . . . . . . . . . . . . . . . . . . . . . 69

402.0 Ventilation Air . . . . . . . . . . . . . . . . . 69

402.1 Occupiable Spaces. . . . . . . . . . . . . 69

402.2 Natural Ventilation Procedure. . . . . 70

Table Minimum Openable Areas:

402.2.1.6(A)(1) Single Openings . . . . . . . . . . . . . . . 71

Table Minimum Openable Areas:

402.2.1.6(A)(2) Two Vertically

Spaced Openings . . . . . . . . . . . . . . 71

402.3 Mechanical Ventilation . . . . . . . . . . 71

402.4 Outdoor Air Intakes. . . . . . . . . . . . . 71

Table 402.4.1 Air Intake Minimum

Separation Distance . . . . . . . . . . . . 72

403.0 Ventilation Rates . . . . . . . . . . . . . . 72

403.1 General. . . . . . . . . . . . . . . . . . . . . . 72

403.2 Zone Calculations. . . . . . . . . . . . . . 73

403.3 Single-Zone Systems . . . . . . . . . . . 73

403.4 One Hundred Percent Outdoor

Air Systems . . . . . . . . . . . . . . . . . . 73

403.5 Multiple-Zone Recirculating Systems . . . . . . . . . . . . . . . . . . . . . 73

403.6 Design for Varying Operating Conditions. . . . . . . . . . . . . . . . . . . . 74

403.7 Exhaust Ventilation. . . . . . . . . . . . . 74

403.8 Dynamic Reset . . . . . . . . . . . . . . . . 75

403.9 Air Classification and

COOLING SYSTEM TYPE	FAN MOTOR SIZE, (hp)	MECHANICAL COOLING CAPACITY, (Btu/h)
DX cooling	Any	≥65 000
Chilled-water and evapo- rative cooling	≥1⁄4	Any

CMC § 403.7.2.3 High relevance — show source text

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

classified as shown in Table 402.1, Table 403.7, or Table 403.9, and its recirculation shall be limited in accordance with Section

403.9.1 through Section 403.9.4. {ASHRAE 62.1:5.18} Recirculated air shall not be taken from prohibited locations in accordance with Section 311.3.

Air (return, transfer, or exhaust air) leaving each space or location shall be designated at an expected air-quality classification not less than that shown in Table 402.1, Table 403.7, or Table 403.9 or as approved by the Authority Having Jurisdiction. Air leaving spaces or locations that are not listed in Table 402.1, Table 403.7, or Table 403.9 shall be designated with the same classification as air from the most similar space or location listed in terms of occupant activities and building construction.

Exception: Air from spaces where environmental tobacco smoke (ETS) is present. (Classification of air from spaces where ETS is present is not addressed. Spaces that are expected to include ETS do not have a classification listed in Table 402.1.)

[ASHRAE 62.1:5.18.1]

TABLE 403.9

AIRSTREAMS OR SOURCES DESCRIPTION AIR CLASS

[ASHRAE 62.1: TABLE 6-3]

DESCRIPTION	AIR CLASS
Kitchen grease hoods	4
Kitchen hoods other than grease	3
Diazo printing equipment discharge	4
Hydraulic elevator machine room	2
Laboratory hoods	4
Paint spray booths	4
~~Refrigerating machinery rooms~~	3

403.9.1 Class 1 Air. Recirculation or transfer of Class 1 air to any space shall be permitted. [ASHRAE 62.1:5.18.3.1]

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 § 160.3 Medium relevance — show source text
e. Excess outdoor air.

viii. The FDD system shall be certified to the Energy Commission as meeting the requirements of Sections 160.3(a)2Hi through 160.3(a)2Hvii in accordance with Section 110.0 and JA6.3. Exception to Section 160.3(a)2Hviii: FDD algorithms based in direct digital control systems are not required to be certified to the Energy Commission. I. Direct digital controls (DDC). Direct digital controls to the zone shall be provided as specified by Table 160.3-C. i. The provided DDC system shall meet the control logic requirements of Sections 160.3(a)2E and 160.3(a)2G, and be capable of the following: ii. Monitoring zone and system demand for fan pressure, pump pressure, heating and cooling; iii. Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers; iv. Automatically detecting the zones and systems that may be excessively driving the reset logic and generate an alarm or other indication to the system operator; v. Readily allow operator removal of zone(s) from the reset algorithm; vi. For new buildings, trending and graphically displaying input and output points; and vii. Resetting heating and cooling setpoints in all noncritical zones upon receipt of a signal from a centralized contact or software point as described in Section 160.3(a)2G. J. Optimum start/stop controls. Space-conditioning systems with DDC to the zone level shall have optimum start/stop controls. The control algorithm shall, as a minimum, be a function of the difference between space temperature and occupied setpoint, the outdoor air temperature, and the amount of time prior to scheduled occupancy. Mass radiant floor slab systems shall incorporate floor temperature onto the optimum start algorithm. Exception to Section 160.3(a)2J: Systems that must operate continuously.

(b) Dwelling unit space-conditioning and air distribution systems.
1. Building cooling and heating loads. Building heating and cooling loads shall be determined using a method based on any one of the following, using cooling and heating loads as two of the criteria for equipment sizing and selection: A. The ASHRAE Handbook, Equipment Volume, Applications Volume and Fundamentals Volume; or B. The SMACNA Residential Comfort System Installation Standards Manual; or
C. The ACCA Manual J.

Exception to Section 160.3(b)1: Block loads, the total load for all rooms combined that are served by the central equipment, may be used for the purpose of system sizing for additions. NOTE: Heating systems are required to have a minimum heating capacity adequate to meet the minimum requirements of the CBC.
1. Design conditions . Design conditions shall be determined in accordance with the following: A. For the purpose of sizing the space-conditioning (HVAC) system, the indoor design temperatures shall be 68°F for heating and 75°F for cooling. B. Outdoor design conditions shall be selected from one of the following: i. Reference Joint Appendix JA2, which is based on data from the ASHRAE Climatic Data for Region X; or ii. The ASHRAE Handbook Fundamentals Volume; or
iii. The ACCA Manual J.

C. The outdoor design temperatures for heating shall be no lower than the 99.0 percent Heating Dry Bulb or the Heating Winter Median of Extremes values.
CMC § 48.0 Medium relevance — show source text
0/48.0)|A3|1000|0.51|2.0| |R-436C|zeotrope|R-290/600a (95.0/5.0)|A3|1000|0.57|2.3| |R-437A|zeotrope|R-125/134a/600/601 (19.5/78.5/1.4/0.6)|A1|990|5.1|––| |R-438A|zeotrope|R-32/125/134a/600/601a (8.5/45.0/44.2/1.7/0.6)|A1|990|4.9|––| |R-439A|zeotrope|R-32/125/600a (50.0/47.0/3.0)|A2|1000|4.7|18.9| |R-440A|zeotrope|R-290/134a/152a (0.6/1.6/97.8)|A2|1000|1.9|7.811| |R-441A|zeotrope|R-170/290/600a/600 (3.1/54.8/6.0/36.1)|A3|1000|0.39|2.0| |R-442A|zeotrope|R-32/125/134a/152a/227ea
(31.0/31.0/30.0/3.0/5.0)|A1|1000|21|––| |R-443A|zeotrope|R-1270/290/600a (55.0/40.0/5.0)|A3|640|0.19|2.2| |R-444A|zeotrope|R-32/152a/1234ze(E) (12.0/5.0/83.0)|A2L|850|5.1|19.9| |R-444B|zeotrope|R-32/152a/1234ze(E) (41.5/10.0/48.5)|A2L|930|4.3|17.3| |R-445A|zeotrope|R-744/134a/1234ze (E) (6.0/9.0/85.0)|A2L|930|4.2|2.7| |R-446A|zeotrope|R-32/1234ze(E)/600 (68.0/29.0/3.0)|A2L|960|2.5|13.510| |R-447A|zeotrope|R-32/125/1234ze(E) (68.0/3.5/28.5)|A2L|960|2.6|18.910| |R-447B|zeotrope|R-32/125/1234ze(E) (68.0/8.0/24.0)|A2L|970|2.6|20.6| |R-448A|zeotrope|R-32/125/1234yf/134a/1234ze(E)
(26.0/26.0/20.0/21.0/7.0)|A1|860|24|––| |R-448B|––|R-32/125/1234yf/134a/1234ze(E)
(21.0/21.0/20.0/31.0/7.0)|A1|850|22.
CMC § 403.5.1.1 Medium relevance — show source text
403.5.1.1 Occupant Diversity. The occupant diversity ratio ( D) shall be determined in accordance with Equation 403.5.1.1 to account for variations in population within the ventilation zones served by the system.

(Equation 403.5.1.1) D = Ps / ∑ all zones Pz

Where the system population ( Ps ) is the total population in the area served by the system.

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VENTILATION AIR

Exception: Alternative methods to account for occupant diversity shall be permitted, provided that the resulting ( Vou ) value is not less than that determined in accordance with Equation 403.5.1.

[ASHRAE 62.1:6.2.4.1.1]

403.5.1.2 System Ventilation Efficiency. The system ventilation efficiency ( Ev ) shall be determined in accordance with Section 403.5.1.3 for the

simplified procedure or Section 404.0 for the alternate procedure. These procedures also establish zone minimum primary airflow rates for VAV systems.

[ASHRAE 62.1:6.2.4.2]

403.5.1.3 Simplified Procedure for System Ventilation Efficiency. System ventilation efficiency ( Ev ) shall be determined in accordance with Equation 403.5.1.3(1) or Equation 403.5.1.3(2).

[ASHRAE 62.1:6.2.4.3 – 6.2.4.3.1]

[Equation 403.5.1.3(1)]

Ev = 0.88 • D + 0.22 for D < 0.60

Ev = 0.75 for D ≥ 0.60 [Equation 403.5.1.3(2)]

403.5.1.4 Zone Minimum Primary Airflow. For each zone, the minimum primary airflow ( Vpz-min ) shall be determined in accordance with Equation 403.5.1.4. [ASHRAE 62.1:6.2.4.3.2]

Vpz-min = Voz• 1.5 (Equation 403.5.1.4)

403.5.2 Outdoor Air Intake. The design outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.5.2. [ASHRAE 62.1:6.2.4.4]

Vot = Vou / Ev (Equation 403.5.2)

403.6 Design for Varying Operating Conditions. Ventilation systems shall be designed to be capable of providing not less than the minimum ventilation rates required in the breathing zone where the zones served by the system are occupied, including all full- and part-load conditions. The minimum outdoor air intake flow shall be permitted to be less than the design value at part-load conditions. [ASHRAE 62.1:6.2.5 – 6.2.5.1]
CMC § 503.5 Medium relevance — show source text
(1) DX and chilled-water cooling units that control the capacity of the mechanical cooling directly based on space temperature shall have a minimum of two stages of fan control. Low or minimum speed shall not exceed 66 percent of full speed. At low or minimum speed, the fan system shall draw no more than 40 percent of the fan power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.

(2) All other units, including DX cooling units and chilled-water units that control the space temperature by modulating the airflow to the space, shall have modulating fan control. Minimum speed shall not exceed 50 percent of full speed. At minimum speed, the fan system shall draw no more than 30 percent of the power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.

(3) Units that include an air economizer to meet the requirements of Section E 503.5 through Section E 503.5.4.1 shall have a minimum of two speeds of fan control during economizer operation.

Exceptions:

(1) Modulating fan control shall not be required for chilled-water and evaporative cooling units with less than 1 hp (0.7 kW) fan motors where the units are not used to provide ventilation air and where the indoor fan cycles with the load.

(2) Where the volume of outdoor air required to meet the ventilation requirements of Chapter 4 or ASHRAE 62.1 at low speed exceeds the air that would be delivered at the speed defined in Section E 503.5.6.2(1), or Section E 503.5.6.2(2), then the minimum speed shall be selected to provide the required ventilation air.

[ASHRAE 90.1:6.5.3.2.1]

TABLE E 503.5.6.2

FAN AIRFLOW CONTROL

[ASHRAE 90.1: TABLE 6.5.3.2.1]

COOLING SYSTEM TYPE FAN MOTOR SIZE,
(hp) MECHANICAL
COOLING CAPACITY,
(Btu/h)

DX cooling Any ≥65 000

Chilled-water and evapo-
rative cooling
≥1⁄4
Any

For SI units: 1000 British thermal units per hour = 0.293 kW, 1 horsepower = 0.746 kW, 1 cubic foot per minute = 0.00047 m [3] /s

E 503.5.6.2.1 VAV Static Pressure Sensor Location. Static pressure sensors used to control VAV fans shall be located such that the controller setpoint is not more than 1.2 inches water column (0.30 kPa). Where this results in the sensor being located downstream of major duct splits, sensors shall be installed in each major branch to ensure that static pressure is maintained in each.

Exception: Systems that are in accordance with Section E 503.5.6.2.2. [ASHRAE 90.1:6.5.3.2.2]
CMC § 7-1 Medium relevance — show source text
d.: Replace Table 7-1, 8-1, 8-2, or 9-1 with Table 4-A.

(5) ASHRAE 170. Section 6.9 -- See also Section 605.2 and 605.3.

(6) ASHRAE 170. Section 7.1a -- Modify as follows:

Replace reference to Table 7-1 with reference to Table 4-A.

(7) ASHRAE 170. Section 7.2.1 c -- Not adopted.

(8) ASHRAE 170. Section 7.2.2 Also see Section 415.0.

(9) ASHRAE 170. Section 7.2.3 -- Not adopted.

(10)ASHRAE 170. Section 7.3.1 -- Modify as follows:

Replace reference to Table 7-1 with reference to Table 4-A.

(11) ASHRAE 170. Section 7.4.1 -- Modify as follows:

Delete the Exception that allows for high return grilles.

(12)ASHRAE 170. Section 8.1a -- Modify as follows: Replace reference to Table 8-1 with reference to Table 4-A.

(13)ASHRAE 170. Section 8.2 -- Modify as follows: Replace reference to Table 8-2 with reference to Table 4-A.

(14)ASHRAE 170. Section 9.1a -- Modify as follows: Replace reference to Table 9-1 with reference to Table 4-A.

2025 CALIFORNIA MECHANICAL CODE 69

), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

VENTILATION AIR

«

«

402.2.1.5 Corner Openings. For zones with operable openings on two adjacent sides of a zone, the distance from the operable openings shall be not more than 5 H along a line drawn between the two openings that are farthest apart. Floor area outside that line shall comply with Section 402.2.1.1 as a zone having openings on only one side of the zone.

[ASHRAE 62.1:6.4.1.5]

402.2.1.6 Location and Size of Openings. Zones or portions of zones to be naturally ventilated shall have a permanently open airflow path to openings directly connected to the outdoors. The minimum flow rate to the zone shall be determined in accordance with

Section 403.2.1. This flow rate shall be used to deter mine the required openable area of openings, accounting only for buoyancy-driven flow. Wind-driven flow shall be used only where it can be demonstrated that the minimum flow rate is provided during all occupied hours. Openings shall be sized in accordance with Section 402.2.1.6(A). Permanently open airflow path shall include, but not be limited to, pathways that would allow airflow unimpeded by partitions, walls, and furnishings. {ASHRAE 62.1:6.4.1.6}

COOLING SYSTEM TYPE	FAN MOTOR SIZE, (hp)	MECHANICAL COOLING CAPACITY, (Btu/h)
DX cooling	Any	≥65 000
Chilled-water and evapo- rative cooling	≥1⁄4	Any

CEC § 403 Medium relevance — show source text

Appendix D Fuel Supply: Manufactured/Mobile Home Parks and Recreational

Vehicle Parks . . . . . . . . . . . . . . . . 403

Appendix E Sustainable Practices . . . . . . . . . . 411

Appendix F Sizing of Venting Systems and Outdoor Combustion and

Ventilation Opening Design . . . . . 533

Appendix G Example Calculation of Outdoor Air Rate. . . . . . . . . . . . . . 545

Appendix H Professional Qualifications . . . . . . 549

Appendix I Indoor Horticultural Facilities . . . . 553

Appendix J Clean Air Delivery. . . . . . . . . . . . . 559

USEFUL TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571

HISTORY NOTE

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

2025 CALIFORNIA MECHANICAL CODE

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

CHAPTER 1 – ADMINISTRATION

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
Chapter/Section
_Division I

CMC § 403.1 Medium relevance — show source text

CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

CHAPTER 4 – SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY AND USE

(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting agency	BSC	BSC- CG	SFM	1	2	1/AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt entire chapter	X							X	X	X	X	X		X	X	X
Adopt entire chapter as amended (amended sections listed below)			X	X	X								X
Adopt only those sections that are listed below						X	X																X
Chapter / Section
403			X
403.1			X
403.1.1			X
403.2			X
403.2.1			X
403.2.1.1			X
403.3			X
403.3.1			X
403.3.1.2			X
403.3.2			X
403.3.2.1			X
403.3.3			X
403.3.5			X
403.4.7			X
403.4.7.1			X
403.4.8.1			X
403.5.4			X
403.6			X
403.7			X
404.5			X
404.6			X
404.12			X
406.2.1			X	X	X
406.

CMC § 1716.5 Medium relevance — show source text
1716.5 Bypass . . . . . . . . . . . . . . . . . . . . . 356

1716.6 Metering . . . . . . . . . . . . . . . . . . . . 356

1717.0 ATL Distributed Energy Systems Design Requirements . . 356

1717.1 Thermal Resources . . . . . . . . . . . 356

1717.2 District Load Profiles. . . . . . . . . . . 357

CHAPTER 18 REFERENCED STANDARDS . . . 359

1801.0 General. . . . . . . . . . . . . . . . . . . . . 361

1801.1 Standards . . . . . . . . . . . . . . . . . . . 361

Table 1801.1 Referenced Standards . . . . . . . . . 361

1801.2 Standards, Publications Practices, and Guides . . . . . . . . . 378

Table 1801.2 Standards, Publications Practices, and Guides . . . . . . . . . 378

xlvi

APPENDICES TABLE OF CONTENTS. . . . . . . . 385

Appendix A Residential Plans Examiner Review Form for HVAC

System Design . . . . . . . . . . . . . . . 387

Appendix B Procedures to be Followed to Place Gas Equipment in Operation . . . . . . . . . . . . . . . . . . . 391

Appendix C Installation and Testing of Oil (Liquid) Fuel-Fired Equipment . . . 395

Appendix D Fuel Supply: Manufactured/Mobile Home Parks and Recreational

Vehicle Parks . . . . . . . . . . . . . . . . 403

Appendix E Sustainable Practices . . . . . . . . . . 411

Appendix F Sizing of Venting Systems and Outdoor Combustion and

Ventilation Opening Design . . . . . 533

Appendix G Example Calculation of Outdoor Air Rate. . . . . . . . . . . . . . 545

Appendix H Professional Qualifications . . . . . . 549

Appendix I Indoor Horticultural Facilities . . . . 553

Appendix J Clean Air Delivery. . . . . . . . . . . . . 559

USEFUL TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571

HISTORY NOTE

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

2025 CALIFORNIA MECHANICAL CODE

), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

CHAPTER 1 – ADMINISTRATION

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

|Adopting

CMC § 403.7 Medium relevance — show source text

1 Table 403.7 Notes 11 & 12	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency Adopt Entire Chapter Adopt Entire Chapter as amended (amended sections listed below) Adopt only those sections that are listed below Chapter/Section 401.1 401.3 401.3.1 402.1 402.1.2 402.2 402.3 403.0 403.7.2.1 – 403.7.2.4 405.3 406.0 407.0 408.0 409.0 410.0 411.0 412.0 413.0 414.0 415.0 416.0 – 416.2 416.3 416.4 417.0 418.0 419.0 Table 4-A Table 4-B Table 4-C Table 402.1 Table 403.7_Notes 11 & 12_	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopting Agency Adopt Entire Chapter Adopt Entire Chapter as amended (amended sections listed below) Adopt only those sections that are listed below Chapter/Section 401.1 401.3 401.3.1 402.1 402.1.2 402.2 402.3 403.0 403.7.2.1 – 403.7.2.4 405.3 406.0 407.0 408.0 409.0 410.0 411.0 412.0 413.0 414.0 415.0 416.0 – 416.2 416.3 416.4 417.0 418.0 419.0 Table 4-A Table 4-B Table 4-C Table 402.1 Table 403.

CMC § 503.7 Medium relevance — show source text
(4) Section E 503.7, “Minimum Equipment Efficiency Tables.” [ASHRAE 90.1:6.2.1]

E 503.2.2 Additional Requirements. Mechanical equipment and systems shall comply with one of the following:

(1) Section E 503.3, “Simplified Approach Building Compliance Path for HVAC Systems”

Exception: When compliance is shown using Section E 503.2.2(1), compliance with Section E 503.4 is not required.

(2) Section E 503.5, “Prescriptive Compliance Path”

Exception: HVAC systems only serving the heating, cooling, or ventilating needs of a computer room with IT equipment load greater than 10 kW (34 000 Btu/h) shall be permitted to comply with Section E 503.4, “Equipment Efficiencies, Verification, and Labeling Requirements” and Section E

503.8, “Alternative Compliance Path, Computer Room Systems.” [ASHRAE 90.1:6.2.2] E 503.3 Simplified Approach Building Compliance Path for HVAC Systems. The simplified approach shall be an optional path for compliance where the following conditions are met:

(1) The building is not more than two stories in height. (2) Gross floor area is less than 25 000 square feet (2322.6 m [2] ).

(3) The HVAC system in the building is in accordance with the requirements listed in Section E 503.3.1. [ASHRAE 90.1:6.3.1] E 503.3.1 Criteria. The HVAC system shall comply with all of the following criteria:

(1) The system serves a single HVAC zone.

(2) The equipment shall comply with the variable flow requirements of Section E 503.5.6.2.

(3) Cooling (where any) shall be provided by a unitary packaged or split-system air conditioner that is either air-cooled or evaporatively cooled, with efficiency that is in accordance with the requirements shown in Table E 503.7.1(1) for air conditioners, Table E 503.7.1(2) for heat pumps, or Table E 503.7.1(4) for packaged terminal and room air conditioners and heat pumps for the applicable equipment category.

(4) The system shall have an air economizer in accordance with Section E 503.5 and Section E 503.4.6.13.

(5) Heating (where any) shall be provided by a unitary packaged or split-system heat pump that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(2) for heat pumps or Table E 503.7.1(4) for packaged terminal and room air conditioners and heat pumps, a fuel-fired furnace that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(5) for furnaces, duct furnaces, and unit heaters, an electric resistance heater, or a baseboard system connected to a boiler that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(6) for boilers.

(6) The system shall comply with the exhaust air energy recovery requirements in accordance with Section E 503.5.10.1.2.

(7) The system shall be controlled by a manual changeover or dual setpoint thermostat.

CEC § 384 Medium relevance — show source text

384 2025 CALIFORNIA MECHANICAL CODE

APPENDICES

The appendices are intended to supplement the provisions of the installation requirements of this code. The definitions in Chapter 2 are also applicable to the appendices.

TABLE OF CONTENTS

Appendix A Page

Residential Plans Examiner Review Form for HVAC System Design..............................................................387

Appendix B

Procedures to be Followed to Place Gas Equipment in Operation..................................................................391

Appendix C

Installation and Testing of Oil (Liquid) Fuel-Fired Equipment ..........................................................................395

Appendix D

Fuel Supply: Manufactured/Mobile Home Parks and Recreational Vehicle Parks ..........................................403

Appendix E

Sustainable Practices ......................................................................................................................................411

Appendix F

Sizing of Venting Systems and Outdoor Combustion and Ventilation Opening Design ..................................533

Appendix G

Example Calculation of Outdoor Air Rate........................................................................................................545

Appendix H

Professional Qualifications ..............................................................................................................................549

Appendix I

Indoor Horticultural Facilities ..........................................................................................................................553

Appendix J

Clean Air Delivery............................................................................................................................................559

2025 CALIFORNIA MECHANICAL CODE 385

386 2025 CALIFORNIA MECHANICAL CODE

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

APPENDIX A – RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SYSTEM DESIGN

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter/Section

CMC § 150.0 Medium relevance — show source text
If the total bending exceeds 90 degrees, one
bend shall be a metal elbow.
Return grille devices shall be labeled in accordance with the requirements in Section 150.0(m)12Biv to disclose the grille’s design airflow rate and a
maximum allowable clean-filter pressure drop of 12.5 Pa (0.05 inches water) for the air filter when tested using ASHRAE Standard 52.2, or as rated
in accordance with AHRI Standard 680 for the design airflow rate for the return grille.|Each return duct length shall not exceed 30 feet and shall contain no more than 180 degrees of bend. If the total bending exceeds 90 degrees, one
bend shall be a metal elbow.
Return grille devices shall be labeled in accordance with the requirements in Section 150.0(m)12Biv to disclose the grille’s design airflow rate and a
maximum allowable clean-filter pressure drop of 12.5 Pa (0.05 inches water) for the air filter when tested using ASHRAE Standard 52.2, or as rated
in accordance with AHRI Standard 680 for the design airflow rate for the return grille.|Each return duct length shall not exceed 30 feet and shall contain no more than 180 degrees of bend. If the total bending exceeds 90 degrees, one
bend shall be a metal elbow.
Return grille devices shall be labeled in accordance with the requirements in Section 150.0(m)12Biv to disclose the grille’s design airflow rate and a
maximum allowable clean-filter pressure drop of 12.5 Pa (0.05 inches water) for the air filter when tested using ASHRAE Standard 52.2, or as rated
in accordance with AHRI Standard 680 for the design airflow rate for the return grille.| |SYSTEM NOMINAL
COOLING CAPACITY
(Ton)*|RETURN DUCT 1
MINIMUM NOMINAL DIAMETER
(inch)|RETURN DUCT 2
MINIMUM NOMINAL DIAMETER
(inch)|MINIMUM TOTAL RETURN
FILTER GRILLE NOMINAL AREA
(inch2)| |1.5|12|10|500| |2.0|14|12|600| |2.5|14|14|800| |3.0|16|14|900| |3.5|16|16|1000| |4.0|18|18|1200| |5.0|20|20|1500| |*Not applicable to systems with nominal cooling capacity greater than 5.0 tons or less than 1.5 tons.|*Not applicable to systems with nominal cooling capacity greater than 5.0 tons or less than 1.5 tons.|*Not applicable to systems with nominal cooling capacity greater than 5.0 tons or less than 1.5 tons.|*Not applicable to systems with nominal cooling capacity greater than 5.0 tons or less than 1.5 tons.|

2025 CALIFORNIA ENERGY CODE 169

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

|TABLE 150.0-D—INFILTRATION EFFECTIVENESS WEATHER AND SHIELDING FACTORS [ASHRAE 62.
CMC § 3-3 Medium relevance — show source text
301 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3

302 Wildland-Urban Interface Area Designations . . . . . .3-3

CHAPTER 4 WILDLAND-URBAN INTERFACE AREA

REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . 4-3

401 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

402 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

403 Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

404 Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7

CHAPTER 5 SPECIAL BUILDING CONSTRUCTION

REGULATIONS . . . . . . . . . . . . . . . . . . . . . . . . 5-3

501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3

502 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3

503 Ignition-Resistant Construction and Material. . . . . .5-3

504 Ignition-Resistant Construction. . . . . . . . . . . . . . . . . .5-4

505 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9

506 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9

507 Replacement or Repair of Roof Coverings. . . . . . . . .5-9

CHAPTER 6 FIRE PROTECTION REQUIREMENTS. . . . . . .6-3

601 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

602 Fire Protection Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

603 Vegetation Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

604 Maintenance of Defensible Space . . . . . . . . . . . . . . . 6-5

Frequently asked questions

What is the single most important control requirement from §§ 403.6 and 403.8?

You may reset outdoor‑air intake and zone airflow as conditions change (dynamic reset, § 403.8), but you must still be able to supply the required breathing‑zone minimum ventilation to any occupied zone at full and part load (design and part‑load capability per § 403.6).

Does § 403.6 allow me to reduce outdoor air to any lower value at part load?

No — § 403.6 permits reducing the outdoor‑air intake below the design value at part load, but the system must still be capable of providing the minimum breathing‑zone ventilation to occupied zones. You must size VAV minimums and OA controls accordingly.

Where are the DCV (CO2 sensor, setpoint, commissioning) rules located?

DCV device requirements, sensor placement, CO2 setpoints and commissioning procedures are given in CMC Appendix E (see E805.6) and the California Energy Code; §§ 403.6 and 403.8 do not list those device‑level details.

Is a fixed minimum damper position “dynamic control”?

No — fixed minimum damper position alone is not considered a dynamic control strategy. The Energy Code and Appendix guidance require dynamic control methods (and measured OA verification) rather than simply setting a fixed minimum damper position.

What should a plan reviewer check to confirm compliance?

Confirm the design-sized Vot and each zone Vpz‑min (Voz × 1.5 where applicable) are documented, that DDC logic or OA damper modulation is shown for reset, and that Appendix E commissioning forms (e.g., DCV/economizer tests) are included where applicable.

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