CMC · California Mechanical Code

Single-zone, 100% outdoor-air, and multiple-zone procedures (when to use each)

Q: When do I use the single‑zone equation instead of the multiple‑zone method?

Use the single‑zone equation when the air handler supplies a mixture of outdoor and recirculated air to only one ventilation zone ; that situation is governed by § 403.3 .

Q: If an air handler serves several zones but supplies only outdoor air, is the multiple‑zone formula required?

No — if the air handler supplies only outdoor air to the zones (no recirculation), use the 100% outdoor‑air procedure: Vot = Σ Voz per § 403.4 .

If one air handler serves only one zone, use the single‑zone formula (§ 403.3). If the handler supplies only outdoor air, sum the zone requirements (§ 403.4). If one or more handlers serve multiple zones with recirculation, calculate the uncorrected outdoor air (Vou) including occupant diversity and per‑area rates, then apply system ventilation efficiency (Ev) per § 403.5 to find the required outdoor intake.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

Use the single‑zone procedure when an air handler (or group of handlers) supplies a mixture of outdoor air and recirculated air to only one ventilation zone — compute the outdoor air intake as Vot = Voz per § 403.3. Use the 100% outdoor‑air procedure when the air handler(s) supply only outdoor air to one or more zones — compute Vot = sum of Voz for all zones served per § 403.4. Use the multiple‑zone recirculating procedure when an air handler supplies a mixture of outdoor and recirculated air to more than one ventilation zone; the intake is calculated from the uncorrected outdoor air (Vou), corrected by system ventilation efficiency (Ev) and occupant diversity (D) per § 403.5. (See the controlling provisions in the California Mechanical Code §§ 403.3, 403.4 and 403.5 for the governing equations and definitions.)

The practical rule: if one handler serves one zone use the single‑zone formula (§ 403.3); if the handler supplies only outdoor air use the 100% OA rule (§ 403.4); otherwise use the multiple‑zone rules with the Vou + Ev adjustments (§ 403.5).

Requirements in detail

Key defined terms (first time bolded): Single‑zone, 100% outdoor‑air, Multiple‑zone recirculating systems, Vot (outdoor air intake flow), Vou (uncorrected outdoor air intake), Ev (system ventilation efficiency), D (occupant diversity ratio), Voz (zone outdoor airflow requirement), Rp, Ra, Az, Pz. These appear in the equations and text of § 403.3, § 403.4, and § 403.5.

Decision table — when to use which procedure

Decision‑relevant dimension	Value / test	What to do (short)	Code reference
Air handler supplies mixture to exactly one ventilation zone	Yes	Use Single‑zone: Vot = Voz	§ 403.3
Air handler(s) supply only outdoor air to one or more zones (no recirculation)	Yes	Use 100% outdoor‑air: Vot = Σ Voz (sum all zones served)	§ 403.4
Air handler supplies mixture of outdoor + recirculated air to more than one zone	Yes	Use Multiple‑zone: compute Vou = D·Σ(Rp·Pz) + Σ(Ra·Az), then correct by Ev per § 403.5	§ 403.5, § 403.5.1
Occupant diversity applies (zones with differing population patterns)	Usually	Compute D per § 403.5.1.1 (D = Ps / ΣPz) or apply allowed alternative methods, but result must not be less than Eq. result	§ 403.5.1.1
Uncertainty in Ev or when using alternate Ev method	Yes/No	Determine Ev via the simplified procedure (403.5.1.3) or use the alternate procedure in § 404.0	§ 403.5.1.2, § 404.0

How the multiple‑zone calculation flows (stepwise)

Calculate each zone outdoor requirement Voz from Table 402.1 using Rp, Ra, Pz, and Az (see Appendix G for a worked single‑zone example).
Compute the uncorrected outdoor air intake: Vou = D·Σ(Rp·Pz) + Σ(Ra·Az) (Equation 403.5.1.1) where D is determined by Equation 403.5.1.1.
Determine Ev (system ventilation efficiency) using the simplified method in § 403.5.1.3 or the alternate calculation in § 404.0; Ev reduces required intake if the distribution/recirculation pattern supplies outdoor air more effectively to the critical zones.
Final required outdoor intake (system intake): apply the Ev correction as required by § 403.5 (the code frames Vou → Vot through Ev; follow the section equations).

Exceptions & special cases

Occupant diversity alternatives: The code allows alternative methods to account for occupant diversity, provided the resulting Vou is not less than the value from Equation 403.5.1; see § 403.5.1.1. Use caution—alternatives must not undercut the Eq. result.
Alternate Ev calculation: If you do not use the simplified Ev in § 403.5.1.3, you may apply the alternative procedure in § 404.0 (system/zone ventilation efficiency and average outdoor air fraction analyses). § 404.0 gives a more detailed, sometimes more favorable, method for Ev.
Testing and balancing: All mechanical ventilation systems must be tested and balanced by a qualified technician per § 403.10 (exceptions for single‑family residential). Ensure measured outdoor airflow matches the certificate of compliance and minimum damper positions are marked/maintained.
Demand‑controlled ventilation (DCV): Where DCV is used, acceptance testing and controls must be verified (see Appendix E — E 805 demand‑control procedures) to ensure OSA dampers modulate properly for single‑zone vs. multiple‑zone behavior. The procedures differ for single‑zone and multiple‑zone systems.

Common mistakes

Applying the single‑zone formula when one handler serves multiple zones — this underestimates required outdoor air (see § 403.3 vs. § 403.5).
Forgetting to include the occupant diversity ratio (D) or using an improper value; the code allows alternative diversity methods only if they do not reduce Vou below the equation result (§ 403.5.1.1).
Ignoring system ventilation efficiency (Ev) and the alternative § 404.0 procedure — using Ev conservatively (Ev = 1.0) is safe but may overstate required outdoor air. See § 403.5.1.2 and § 404.0 for proper application.
Not performing required testing and balancing (per § 403.10) or failing DCV acceptance tests in Appendix E (E 805). These are mandatory verification steps.

Worked example — concrete multiple‑zone scenario

Scenario: One air handler serves two zones.

Zone A: Pz = 20 people, Az = 1,000 ft²
Zone B: Pz = 50 people, Az = 2,000 ft²

Use the example zone rates from the Appendix example (Table 402.1 values used there): Rp = 5 cfm/person, Ra = 0.06 cfm/ft² (these are the same rates used in the Appendix G illustration).

Step 1 — zone totals:

Σ(Rp·Pz) = 5 · (20 + 50) = 5 · 70 = 350 cfm
Σ(Ra·Az) = 0.06 · (1,000 + 2,000) = 0.06 · 3,000 = 180 cfm

Step 2 — occupant diversity (use § 403.5.1.1): choose a system population Ps = 50 (e.g., estimated or measured peak for the system). Then D = Ps / ΣPz = 50 / 70 = 0.714.

Step 3 — compute Vou (Eq. 403.5.1.1):

Vou = D·Σ(Rp·Pz) + Σ(Ra·Az) = 0.714·350 + 180 ≈ 250 + 180 = 430 cfm.

Step 4 — apply Ev: if you determine Ev per § 403.5.1.3 or § 404.0, divide Vou by Ev to get required Vot. If you conservatively assume Ev = 1.0 (no efficiency gain), then:

Vot = Vou / Ev = 430 / 1.0 = 430 cfm (system outdoor intake).

Notes: This example follows Equations in § 403.5.1 for Vou and uses the Rp/Ra values illustrated in Appendix G. For an actual design you must compute Ev using the simplified or alternate procedures in the code rather than assume Ev = 1.0 unless justified.

Related provisions

§ 403.10 — Air balance and testing (system testing and balancing requirements).
§ 404.0 — Alternative procedure for multiple‑zone systems ventilation efficiency (detailed Ev and zone Evz methods).
Table 402.1 and Appendix G — zone Rp / Ra values and a worked single‑zone example used for zone Voz calculations.
Appendix E (E 805) — Demand‑controlled ventilation detection/acceptance procedures that differ for single‑zone vs multiple‑zone systems.

Code references

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

CMC § 403.3 High relevance — show source text
403.3 Single-Zone Systems. For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to only one ventilation zone, the outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.3. [ASHRAE 62.1:6.2.2]

Vot = Voz (Equation 403.3)

403.4 One Hundred Percent Outdoor Air Systems. For ventilation systems where one or more air handlers supply only outdoor air to one or more ventilation zones, the outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 403.4. [ASHRAE 62.1:6.2.3]

Vot = ∑ all zones Voz (Equation 403.4)

403.5 Multiple-Zone Recirculating Systems. For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to more than one ventilation zone, the outdoor air intake flow ( Vot ) shall be determined in accordance with Section 403.5.1 through Section 403.5.2. [ASHRAE 62.1:6.2.4]

403.5.1 Uncorrected Outdoor Air Intake. The uncorrected outdoor air intake ( Vou ) flow shall be determined in accordance with Equation 403.5.1. [ASHRAE 62.1:6.2.4.1]

(Equation 403.5.1) Vou = D ∑ all zones ( Rp•Pz ) + ∑ all zones ( Ra•Az )

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).
California Mechanical Code High relevance — show source text
**|Step 1: Simulate a signal at or slightly above the CO2 setpoint or follow manufacturers recommended testing proce-
dures.|Step 1: Simulate a signal at or slightly above the CO2 setpoint or follow manufacturers recommended testing proce-
dures.|Step 1: Simulate a signal at or slightly above the CO2 setpoint or follow manufacturers recommended testing proce-
dures.| |
For single zone units, outdoor air damper modulates opens to satisfy the total ventilation air called for in the certificate
of compliance.|
For single zone units, outdoor air damper modulates opens to satisfy the total ventilation air called for in the certificate
of compliance.|
For single zone units, outdoor air damper modulates opens to satisfy the total ventilation air called for in the certificate
of compliance.|
For single zone units, outdoor air damper modulates opens to satisfy the total ventilation air called for in the certificate
of compliance.| |
For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation
requirements.|
For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation
requirements.|
For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation
requirements.|
For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation
requirements.| |Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.| |
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.| |
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

| |Step 3: System returned to initial operating conditions.|Y/N|Y/N|Y/N|
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 § 25.4 High relevance — show source text

|
For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation
requirements.| |Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.|Step 2: Simulate signal well below the CO2 setpoint or follow manufacturers recommended procedures.| |
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.|
For single zone units, outdoor air damper modulates to the design minimum value.| |
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

|
For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation
requirements.

| |Step 3: System returned to initial operating conditions.|Y/N|Y/N|Y/N|

B. Testing Results.	PASS / FAIL	Col3
Step 1: Simulate a high CO2 load (check box complete).
Step 2: Simulate a low CO2 load (check box complete).

For SI units: 1 inch = 25.4 mm

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APPENDIX E

CERTIFICATE OF ACCEPTANCE MECH-6A	Col2
Demand Control Ventilation Systems Acceptance (Page 3 of 3)	Demand Control Ventilation Systems Acceptance (Page 3 of 3)
Project Name/Address:	Project Name/Address:
System Name or Identification/Tag:	System Location or Area Served:

C.	PASS/FAIL Evaluation (check one):
	PASS: AllConstruction Inspection responses are complete andTesting Results responses are “Pass.”
	FAIL: AnyConstruction Inspection responses are incomplete_OR_ there is one or more “Fail” responses inTesting Results section. Provide explanation below. Use and attach additional pages if necessary.

2025 CALIFORNIA MECHANICAL CODE 507

CMC § 1.11.0. High relevance — show source text
This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

2025 CALIFORNIA MECHANICAL CODE 545

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546 2025 CALIFORNIA MECHANICAL CODE

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»

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APPENDIX G

EXAMPLE CALCULATION OF OUTDOOR AIR RATE

The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.

G 101.0 Example Calculation of Outdoor Air Rate.

G 101.1 Example Calculation. Determine the outdoor air rate required for a single zone AC unit serving an interior 2000 square feet (185.81 m [2] ) conference/meeting room with a design occupancy of 100 people. The system supplies and returns air from the ceiling. (See Chapter 4 of this code for guidelines)

Solution:

In accordance with Table 403.2.2, the zone air distribution effectiveness is 1.0 since the system supplies cooling only from the ceiling. Using the rates from Table 402.1 for a conference/meeting room, the minimum system outdoor air rate is calculated to be:

RpPz + RaAz Vot = (Equation G 101.1) Ez

5 x 100 + 0.06 x 2000

= 1.0

= 620 CFM

Where:

Az = zone floor area: the net occupiable floor area of the zone in square feet (m [2] ).

Pz = zone population: The largest number of people expected to occupy the zone during typical usage. Where the number of people expected to occupy the zone fluctuates, Pz shall be permitted to be estimated based on averaging approaches described in Section 403.6.1. Where Pz cannot be accurately predicted during design, it shall be estimated based on the zone floor area and the default occupant density in accordance with Table 402.1. Rp = outdoor airflow rate (CFM) (L/s) required per person in accordance with Table 402.1 .

Ra = outdoor airflow rate required per unit area (CFM/ft [2] )

[(L/s)/m [2] ] in accordance with Table 402.1.

Ez = zone air distribution effectiveness in accordance with Table 403.2.2. For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s,

1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot

= 5.08 [(L/s)/m [2] ]

RpPz + RaAz Vot = Ez

5 x 100 + 0.06 x 2000

= 1.0

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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

2025 CALIFORNIA MECHANICAL CODE 485

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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.
California Mechanical Code High relevance — show source text
3/8″
main reinforcement bars at 57/8″ pitch
with7/8″ concrete cover;3/8″ main rein-
forcement bars at 41/2″ pitch
perpendicular with1/2″ concrete cover;
13′1″ span restrained.|195 psf|4 hrs|||7|1, 7|4| |F/C-4-RC-7|4″|4″ (5025 psi) concrete deck;1/4″ reinforce-
ment bars at 71/2″ pitch with3/4″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|1 hr
16 min|||7|1, 2|11/4| |F/C-4-RC-8|4″|4″ thick (4905 psi) deck;1/4″ reinforce-
ment bars at 71/2″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|100 psf|1 hr
23 min|||7|1, 2|11/3| |F/C-4-RC-9|4″|4″ deep (4370 psi);1/4″ reinforcement bars
at 6″ pitch with3/4″ cover;1/4″ main rein-
forcement bars at 4″ pitch perpendicular
with1/2″ cover; 13′1″ span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-10|4″|4″ thick (5140 psi) deck;1/4″ reinforce-
ment bars at 71/2″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|1 hr
16 min|||7|1, 5|11/4| |F/C-4-RC-11|4″|4″ thick (4000 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
with top surface; 4″ × 6″ x 13 SWG mesh
reinforcement 1″ from bottom of slab; 6′6″
span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-12|4″|4″ deep (2380 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.
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
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 § 0.0283 High relevance — show source text
For SI units: 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] ], 1 square foot = 0.0929 m [2]

Where:

Vbz = breathing zone outdoor airflow, per Table 402.1. Az = zone floor area, the net occupiable floor area of the ventilation zone. W S = aggregated width of all single outdoor openings located at the same elevation.

H S = vertical dimension of the single opening or the least vertical dimension of the openings where there are multiple openings.
- Volumetric airflow rates used to estimate required openable area are based on the following:
- Dry-air density of 0.075 lbda/ft [3] (1.2 kgda/m [3] ) at a barometric pressure of 1 atm (101.3 kPa) and an air temperature of 70°F (21°C)
- Temperature difference between indoors and outdoors of 1.8°F (1°C)
- Gravity constant of 32.2 ft/s [2] (9.81m/s [2] )
- Window discharge coefficient of 0.6
(2) Determine the effect of pressure losses along natural ventilation airflow paths on the resulting flow rates, including inlet openings, air transfer grills, ventilation stacks, and outlet openings during representative conditions of expected natural ventilation system use.

(3) Quantify natural ventilation airflow rates of identified airflow paths accounting for wind induced and thermally induced driving pressures during representative conditions of expected natural ventilation system use.

(4) Design to provide outdoor air in quantities sufficient to result in acceptable IAQ as established under Section 403.2.1 or ASHRAE 62.1 during representative conditions of expected natural ventilation system use. {ASHRAE 62.1:6.4.2}

402.2.3 Control and Accessibility. The means to open required operable openings shall be readily accessible to building occupants whenever the space is occupied. Controls shall be designed to coordinate operation of the natural and mechanical ventilation systems.

[ASHRAE 62.1:6.4.3]

402.3 Mechanical Ventilation. [Not permitted for OSHPD 1, 2, 3, 4 & 5] Where natural ventilation is not permitted by this section or the California Building Standards Code, mechanical ventilation systems shall be designed, constructed, and installed to provide a method of supply air and either return air or exhaust air, or both, as applicable. Mechan

|Col1|TABLE 402.2.1.6(A)(2) MINIMUM OPENABLE AREAS: TWO VERTICALLY SPACED OPENINGS* [ASHRAE 62.
CMC § 402.2.1.6 High relevance — show source text
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

Recirculation. . . . . . . . . . . . . . . . . . 75

Table 403.9 Airstreams or Sources

Description Air Class . . . . . . . . . . . 75

403.10 Air Balance . . . . . . . . . . . . . . . . . . . 75

404.0 Alternative Procedure for

Multiple-Zone Systems Ventilation Efficiency . . . . . . . . . . . 76

xxx

404.1 System Ventilation Efficiency . . . . . 76

404.2 Average Outdoor Air Fraction. . . . . 76

404.3 Zone Ventilation Efficiency . . . . . . . 76

405.0 Ventilation for Residential

Occupancies. . . . . . . . . . . . . . . . . . 77

405.1 General. . . . . . . . . . . . . . . . . . . . . . 77

405.2 Ventilation Air Rate. . . . . . . . . . . . . 77

405.3 Bathroom Exhaust . . . . . . . . . . . . . 77

405.4 Kitchen Exhaust . . . . . . . . . . . . . . . 77

405.5 Ventilation Openings . . . . . . . . . . . 77

406.0 Evaporative Cooling System for Health Care Facilities . . . . . . . . 78

407.0 Ventilation System Details . . . . . . . 78

407.1 General. . . . . . . . . . . . . . . . . . . . . . 78

407.2 Outdoor Air Intakes and
CMC § 4.00 Medium relevance — show source text
10
wood screw|1|24|4.00|0.90|DR|DR|2.85|DR|DR|DR| |Minimum 1x
Wood Furringd|Minimum 2x
Wood Stud|1/4" lag screw|11/2|12|4.00|2.65|1.50|0.90|4.00|1.65|0.80|DR| |Minimum 1x
Wood Furringd|Minimum 2x
Wood Stud|1/4" lag screw|11/2|16|4.00|1.95|0.95|0.50|4.00|1.10|DR|DR| |Minimum 1x
Wood Furringd|Minimum 2x
Wood Stud|1/4" lag screw|11/2|24|4.00|1.10|DR|DR|3.25|0.50|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood framing and furring shall be spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with ANSI/AWC NDS.
b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required
penetration into framing.
d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2-inch nominal wood furring or an
approved design shall be used.
e. Foam sheathing shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289.
f. Furring shall be spaced not greater than 24 inches on center in a vertical or horizontal orientation. In a vertical orientation, furring shall be located over wall studs and attached with
the required fastener spacing. In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs at 16 inches
and 24 inches on center, respectively.|For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood framing and furring shall be spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with ANSI/AWC NDS.
b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required
penetration into framing.
d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2-inch nominal wood furring or an
approved design shall be used.
e.

Frequently asked questions

When do I use the single‑zone equation instead of the multiple‑zone method?

Use the single‑zone equation when the air handler supplies a mixture of outdoor and recirculated air to only one ventilation zone; that situation is governed by § 403.3.

If an air handler serves several zones but supplies only outdoor air, is the multiple‑zone formula required?

No — if the air handler supplies only outdoor air to the zones (no recirculation), use the 100% outdoor‑air procedure: Vot = Σ Voz per § 403.4.

What is the purpose of the occupant diversity factor (D)?

D reduces the aggregate people component when not all zones are expected to be at peak occupancy simultaneously. Compute D per § 403.5.1.1 or use an alternative method only if it does not reduce Vou below the equation result.

Where does **Ev** come from and can I use a standard default?

Ev (system ventilation efficiency) must be determined per the simplified procedure § 403.5.1.3 or via the alternate, more detailed analysis in § 404.0. Using a default (e.g., Ev = 1.0) is conservative but may not be the most efficient or code‑compliant approach unless justified.

Do I have to test and balance measured outdoor airflow?

Yes — mechanical ventilation systems must be tested and balanced in accordance with § 403.10 (exceptions for single‑family residential), and DCV systems have specific acceptance testing in Appendix E.

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California Mechanical Code