CMC · California Mechanical Code
Design for varying operating conditions and averaging time provisions
You can size ventilation for short occupancy spikes by averaging over a code formula time T (T = 3·zone volume / breathing‑zone airflow) and you may use dynamic reset of outdoor and zone airflows — but the average ventilation delivered over T (and flows when occupied) must meet the breathing‑zone minimums required by the CMC (see §§ 403.6 and 403.8).
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Ventilation systems must be able to provide the required minimum ventilation rates in the breathing zone under all occupied conditions, including full- and part‑load. The code permits designing with time‑averaging for short‑term peaks and allows the outdoor air intake and zone airflows to be reset as operating conditions change. See § 403.6 and § 403.8 for the controlling rules.
The most important rule: where short spikes in occupancy or short interruptions occur you may design using an averaging period T (calculated by the code) so that the average outdoor/breathing‑zone airflow over T meets the required breathing‑zone rate.
Key defined terms (first mention bolded)
- Averaging time (T) — the period over which outdoor/breathing‑zone flows or occupant counts may be averaged (see Equation § 403.6.1).
- Breathing zone outdoor airflow (Vbz) — the airflow required to serve the breathing zone (computed per Equation § 403.2.1).
- Minimum outdoor air intake (Vot) — the system outdoor‑air intake flow determined by the applicable design procedure (single‑zone, 100% OA, or multiple‑zone).
- Zone population (Pz) and zone volume (v) — inputs to the averaging time equation.
Requirements in detail
1) Basic capability and part‑load allowance
- Systems must be capable of supplying at least the minimum ventilation rates in the breathing zone whenever the zones served are occupied (full- and part‑load). § 403.6 authorizes that the minimum outdoor air intake flow may be less than the design value at part‑load.
2) Averaging for short‑term conditions (how to size using T)
- When peak occupancy is short, or ventilation is varied/interrupted for a short time, the designer may base the design on the average conditions over an averaging time T computed by the code. The code gives the formula:
- T = 3·v / Vbz (minutes) — Equation in § 403.6.1.
- Acceptable adjustments when using this provision:
- Pz (zone population) may be averaged over T for zones with fluctuating occupancy.
- If supply air is intermittently interrupted, the average outdoor airflow to the breathing zone over T must be at least Vbz.
- If the outdoor‑air intake is intermittently closed, the average outdoor air intake over T must be at least the minimum outdoor air intake (Vot).
3) Dynamic reset permission
- Designers are explicitly permitted to use reset strategies that change Vot and/or Voz (space or zone airflow) as operating conditions change (for example, occupancy, load, or other signals). This permission appears in § 403.8. Note this is a permission — the code does not prescribe a single reset algorithm.
Decision‑relevant dimensions and values
| Decision dimension | Typical values / formula | Effect on design | Code reference |
|---|---|---|---|
| Averaging time T | T = 3·v / Vbz (minutes) | Use T to compute time‑averaged Pz, average outdoor airflow to breathing zone, or average outdoor intake for intermittent operation. | § 403.6.1 |
| Breathing‑zone flow Vbz | Calculated per § 403.2.1 (use zone population or default occupancy) | Determines minimum required average outdoor airflow over T and sets denominator in T formula. | § 403.2.1 (see referenced calculation) |
| Minimum outdoor intake Vot | Determined by single‑zone (§ 403.3), 100% OA (§ 403.4), or multiple‑zone (§ 403.5) procedures | If intake is intermittently closed, its time‑average over T must be ≥ Vot. | § 403.3 / § 403.4 / § 403.5 |
| Reset of Vot / Voz | Allowed (no single required algorithm) | Designer may implement dynamic controls to lower or raise flows as conditions change, but must ensure breathing‑zone requirements are met when occupied. | § 403.8 |
(Where specific formulas for Vbz and Vot are needed, reference the zone calculation and system intake sections of Chapter 4: § 403.2.1, § 403.3, § 403.4, and § 403.5.)
Exceptions & special cases
- Short‑duration peaks: you may use the averaging provision in § 403.6.1 when peak occupancy or interruptions are short and known.
- Part‑load operation: the code explicitly allows the minimum outdoor air intake to be less than the design value during part‑load operation, provided zone breathing‑zone requirements are met when occupied. § 403.6 allows this.
- Reset strategies: § 403.8 permits resetting Vot and/or Voz; the code does not mandate a specific sensor/algorithm — but the chosen strategy must still meet breathing‑zone minimums (and other applicable code requirements).
If you plan to rely on other parts of the code (for example, the multiple‑zone ventilation efficiency methods, occupant diversity calculations, or specific outdoor‑air intake equations), be sure to follow those sections (e.g., § 403.5.1 and § 403.5.2) when computing design Vot and related quantities.
Common mistakes
- Assuming a fixed short averaging window without computing T from the room volume (v) and Vbz — the code requires the specific formula in § 403.6.1.
- Averaging only occupancy but not verifying the average outdoor airflow over T meets Vbz — both the population and the actual delivered outdoor air must meet the averaging criteria.
- Using a simple fixed minimum damper position and calling that a dynamic reset — § 403.8 permits resets, but a fixed minimum damper is not the same as an actively controlled reset strategy (and may not satisfy other code or energy‑code dynamic control expectations).
- Forgetting to verify that part‑load reductions still meet breathing‑zone requirements when the zone is actually occupied — the basic mandate in § 403.6 remains.
Worked example — conference room with short peak occupancy
Scenario: A conference room is 40 ft × 30 ft × 10 ft high → zone volume v = 12,000 ft³. Design breathing‑zone outdoor airflow for the room (Vbz) is computed during the zone calculation step as Vbz = 200 cfm (assumed from zone occupant rates / formula). Use the code averaging provision to find T.
Step 1 — compute averaging time:
- T = 3·v / Vbz = 3 × 12,000 ft³ / 200 cfm = 36,000 / 200 = 180 minutes. (Use § 403.6.1 formula.)
Implications:
- If the room occasionally has a 30‑minute presentation with double the usual people, you may design using time‑averaged occupancy over T = 180 min; i.e., the averaged Pz over those 180 minutes is used in sizing instead of the short 30‑minute peak, provided the average outdoor air delivered to the breathing zone over the 180‑minute period is at least Vbz = 200 cfm.
- If the outdoor air intake is closed for, say, a 10‑minute period (e.g., economizer disabled briefly), the system must provide enough outdoor air during the remaining 170 minutes so that the average outdoor intake over the 180‑minute T is at least the required Vot (the minimum outdoor air intake calculated for the system).
Worked‑example note: the Vbz and Vot values must be calculated per the zone and system procedures in Chapter 4 (see § 403.2.1, § 403.3, § 403.4, § 403.5). The averaging provision does not change how Vbz or Vot are computed — it only allows averaging over T to address short‑term fluctuations.
Related provisions (CMC sections)
- § 403.2.1 — breathing‑zone outdoor airflow calculation (used in the T formula).
- § 403.3 — single‑zone system outdoor‑air intake sizing (Vot).
- § 403.4 — 100% outdoor‑air systems (Vot basis).
- § 403.5 / § 403.5.1 — multiple‑zone systems and system ventilation efficiency (affects Vot).
- § 403.6.1 — averaging time formula and acceptable design adjustments (see above).
- § 403.8 — permission to use dynamic reset of Vot and Voz as operating conditions change.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 62.1 High relevance — show source text
[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]
403.6.1 Short-Term Conditions. Where it is known that peak occupancy will be of short duration, ventilation will be varied or interrupted for a short period of time, or both, the design shall be permitted to be based on the average conditions over a time period ( T ) determined by Equation 403.6.1.
T = 3 v/Vbz (Equation 403.6.1)
Where:
T = averaging time period, minutes.
v = the volume of the ventilation zone where averaging is being applied, ft [3] (m [3] ).
Vbz = the breathing zone outdoor airflow calculated in accordance with Equation 403.2.1 and design value of the zone population ( Pz ), cubic foot per minute (CFM).
For SI Units: 1 cubic foot = 0.0283 m [3], 1 cubic foot per minute =
0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
Acceptable design adjustments based on this optional provision including the following:
(1) Zones with fluctuating occupancy: The zone population ( Pz ) shall be permitted to be averaged over time ( T ).
(2) Zones with intermittent interruption of supply air: The average outdoor airflow supplied to the breathing zone over time ( T ) shall be not less than the breathing zone outdoor airflow ( Vbz ) calculated using Equation 403.2.1.
(3) Systems with intermittent closure of the outdoor air intake: The average outdoor air intake over time ( T ) shall be not less than the minimum outdoor air intake ( Vot ) calculated using Equation 403.3, Equation 403.4, or Equation 403.5.1 as applicable.
CMC § 403.6.1 High relevance — show source text
T = 3 v/Vbz (Equation 403.6.1)
Where:
T = averaging time period, minutes.
v = the volume of the ventilation zone where averaging is being applied, ft [3] (m [3] ).
Vbz = the breathing zone outdoor airflow calculated in accordance with Equation 403.2.1 and design value of the zone population ( Pz ), cubic foot per minute (CFM).
For SI Units: 1 cubic foot = 0.0283 m [3], 1 cubic foot per minute =
0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
Acceptable design adjustments based on this optional provision including the following:
(1) Zones with fluctuating occupancy: The zone population ( Pz ) shall be permitted to be averaged over time ( T ).
(2) Zones with intermittent interruption of supply air: The average outdoor airflow supplied to the breathing zone over time ( T ) shall be not less than the breathing zone outdoor airflow ( Vbz ) calculated using Equation 403.2.1.
(3) Systems with intermittent closure of the outdoor air intake: The average outdoor air intake over time ( T ) shall be not less than the minimum outdoor air intake ( Vot ) calculated using Equation 403.3, Equation 403.4, or Equation 403.5.1 as applicable.
[ASHRAE 62.1:6.2.5.2]
403.7 Exhaust Ventilation. Exhaust airflow shall be provided in accordance with the requirements in Table 403.7. Exhaust makeup air shall be permitted to be a combination of outdoor air, recirculated air, and transfer air.
403.7.1 Parking Garages. Exhaust rate for parking garages shall be in accordance with Table 403.7. Exhaust rate shall not be required for enclosed parking garages having a floor area of 1000 square feet (92.9 m [2] ) or less and used for the storage of 5 or less vehicles.
403.7.2 Enclosed Parking Garages. Mechanical ventilation systems for enclosed parking garages shall operate continuously.
Exceptions:
(1) Mechanical ventilation systems shall be permitted to operate intermittently where the system is designed to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.
(2) Approved automatic carbon monoxide sensing devices, and nitrogen dioxide detectors shall be permitted to modulate the ventilation system to not exceed a maximum average of 50 parts per million of carbon monoxide, or 1 part per million nitrogen dioxide during an eight-hour period with a concentration of not more than 200 parts per million for carbon monoxide, or 5 parts per million nitrogen dioxide, for a period not exceeding 15 minutes. Automatic sens
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VENTILATION AIR
ing devices installed in modulated parking garage ventilation systems shall be approved in accordance with Section 301.2.
403.7.2.1 Alternative Exhaust Ventilation for Enclosed Parking Garages.
CMC § 1.0 High relevance — show source text
= 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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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
APPENDIX H – PROFESSIONAL QUALIFICATIONS
(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.)
CMC § 1.11.0. Medium 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.
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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 § 303.10.1 Medium 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 § 402.2.1.6 Medium 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 § 805.8 Medium relevance — show source text
At full flow:
(1) Supply fan maintains discharge static pressure within plus or minus 10 percent of the current operating control static pressure setpoint. (2) Supply fan controls stabilizes within a 5 minute period. (3) At minimum flow (not less than 30 percent of total design flow). (4) Supply fan controls modulate to decrease capacity. (5) Current operating setpoint has decreased (for systems with DDC to the zone level). (6) Supply fan maintains discharge static pressure within plus or minus 10 percent of the current operating setpoint. E 805.8 Valve Leakage (Form MECH-8A). The purpose of this test is to ensure that control valves serving variable flow systems are designed to withstand the pump pressure over the full range of operation. Valves with insufficient actuators will lift under certain conditions causing water to leak through and loss of control. This test applies to the variable flow systems, chilled and hot-water variable flow systems, chiller isolation valves, boiler isolation valves, and watercooled air conditioner and hydronic heat pump systems.
E 805.8.1 Test Procedure. The procedure for performing a functional test for valve leakage shall be in accordance with Section E 805.8.1.1 and Section E
805.8.1.2.
E 805.8.1.1 Construction Inspection. Prior to functional testing, verify and document the valve and piping arrangements were installed in accordance with the design drawings. E 805.8.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:
Step 1: For each pump serving the distribution system, dead head the pumps using the discharge isolation valves at the pumps. Document the following:
(1) Record the differential pressure across the
pumps.
(2) Verify that this is within 5 percent of the submittal data for the pump.
Step 2: Reopen the pump discharge isolation valves. Automatically close valves on the systems being tested. Where three-way valves are present, close off the bypass line. Verify and document the following:
(1) The valves automatically close.
(2) Record the pressure differential across the
pump.
(3) Verify that the pressure differential is within 5 percent of the reading from Step 1 for the pump that is operating during the valve test.
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APPENDIX E
Step 3: Restore system to correct operating conditions.
E 805.8.2 Acceptance Criteria. System has no flow where coils are closed and the pump is turned on. E 805.9 Supply Water Temperature Reset Controls (Form MECH-9A). The purpose of this test is to ensure that both the chilled water and hot water supply temperatures are automatically reset based on either building loads or outdoor air temperature, as indicated in the control sequences. Many HVAC systems are served by central chilled and heating hot water plants. The supply water operating temperatures shall meet peak loads where the system is operating at design conditions. As the loads vary, the supply water temperatures shall be permitted to be adjusted to satisfy the new operating conditions. The chilled water supply temperature shall be permitted to be raised as the cooling load decreases, and heating hot water supply temperature shall be permitted to be lowered as the heating load decreases.
CMC § 62.2 Medium relevance — show source text
[ASHRAE 62.2:4.5.1]
E 605.1.7.2 Scheduled Ventilation. This section shall only be used when one or more fixed patterns of designed ventilation are known at the time compliance to Section E 605.0 is being determined. Such patterns include those both clock-driven and driven by typical meteorological data. Compliance with this section shall be demonstrated with either Section E 605.1.7.2.1 or Section E 605.1.7.2.2. [ASHRAE 62.2:4.5.2] E 605.1.7.2.1 Annual Average Schedule. An annual schedule of ventilation complies with this section when the annual average relative exposure is no more than one, and the peak relative exposure shall not exceed five for any time step as calculated in accordance with ASHRAE 62.2. [ASHRAE 62.2:4.5.2.1] E 605.1.7.2.2 Block Scheduling. The schedule of ventilation complies with this section if it is broken into blocks of time and each block individually has an average relative exposure during occupied periods that is no more than one as calculated in ASHRAE 62.2. All blocks shall end with a relative exposure less than or equal to one. [ASHRAE 62.2:4.5.2.2]
E 605.1.7.3 Real-Time Control. A real-time ventilation controller complies with this section when it is designed to adjust the ventilation system based on real-time input to the ventilation calculations so that the average relative exposure during occupied periods is no more than one, and the peak relative exposure shall not exceed five for any time step as calculated in ASHRAE 62.2. The averaging period shall be no more than one year and shall be based on simple, recursive or running average, but not extrapolation.
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E 605.1.3.4(D) Effective Annual Average Infil- tration Rate. Effective Annual Average Infiltration Rate ( Qinf ) shall be calculated using Equation E 605.1.3.4(D):
[Equation E 605.1.3.4(D)]
= [NL] [ • ] [wsf] [ • ] [A][f][loor] Qinf (CFM) 7.3
Where:
NL = normalized leakage wsf = weather and shielding factor from ASHRAE 62.2 Afloor = floor area of residence, ft [2 ]
For SI units: 1 cubic foot per minute = 0.4719 L/s
[ASHRAE 62.2:4.1.2.2] E 605.1.3.5 Different Occupant Density. Table E 605.1.3.1 and Equation E 605.1.3.1 assume two persons in a studio or one-bedroom dwelling unit and an additional person for each additional bedroom. Where higher occupant densities are known, the rate shall be increased by 7.5 ft [3] /min (0.003 m [3] /s) for each additional person. Where approved by the Authority Having Jurisdiction, lower occupant densities shall be permitted to be used. [ASHRAE 62.2:4.1.3] **E 605.1.4 System Type.
CMC § 90.1 Medium relevance — show source text
Exception: Units employing fluid economizers.
[ASHRAE 90.1:6.5.4.5.1]
E 503.5.7.5.1 Controls. Hydronic heat pumps and water-cooled unitary air-conditioners having a total pump system power exceeding 5 hp (3.7 kW) shall have controls, devices, or both (such as variable speed control) that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent of design water flow. [ASHRAE 90.1:6.5.4.5.2]
E 503.5.7.6 Pipe Sizing. Chilled-water and condenser-water piping shall be designed such that the design flow rate in each piping segment shall not exceed the values listed in Table E 503.5.7.6 for the
appropriate total annual hours of operation. Piping size selections for systems that operate under variable flow conditions (e.g., modulating two-way control valves at coils) and that contain variable-speed pump motors shall be permitted to be made from the “Variable Flow/Variable Speed” columns. All others shall be made from the “Other” columns.
Exceptions:
(1) Design flow rates exceeding the values in Table E 503.5.7.6 shall be permitted in specific sections of piping if the piping in question is not in the critical circuit at design conditions and is not predicted to be in the critical circuit during more than 30 percent of operating hours.
TABLE E 503.5.7.6 PIPING SYSTEM DESIGN MAXIMUM FLOW RATE (gallons per minute)
[ASHRAE 90.1: TABLE 6.5.4.6]
OPERATING HOURS/YEAR ≤2000 HOURS/YEAR Col3 >2000 AND ≤4400 HOURS/YEAR Col5 >4400 HOURS/YEAR Col7 NOMINAL PIPE SIZE,
(inches)OTHER VARIABLE FLOW/
VARIABLE SPEEDOTHER VARIABLE FLOW/
VARIABLE SPEEDOTHER VARIABLE FLOW/
VARIABLE SPEED21⁄2 120 180 85 130 68 110 3 180 270 140 210 110 170 4 350 530 260 400 210 320 5 410 620 310 470 250 370 6 740 1100 570 860 440 680 8 1200 1800 900 1400 700 1100 10 1800 2700 1300 2000 1000 1600 12 2500 3800 1900 2900 1500 2300 Maximum velocity for pipes over
14-24 inches in size8.5 ft/s 13.0 ft/s 6.5 ft/s 9.5 ft/s 5.0 ft/s 7.5 ft/s For SI units: 1 gallon per minute = 0.06 L/s, 1 foot per second = 0.3048 m/s, 1 inch = 25.4 mm
2025 CALIFORNIA MECHANICAL CODE 441
«
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.
2025 CALIFORNIA MECHANICAL CODE 73
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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]
California Mechanical Code Medium relevance — show source text
IN THOUSANDS OF BTU PER HOUR**|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|262
271
279|293
331
361|183
219
247|325
334
344|373
422
462|234
281
316|447
458
468|463
524
574|286
344
385| |8|1
2
3|285
293
302|316
353
381|191
228
256|352
360
370|403
450
489|244
292
328|481
492
501|502
560
609|299
355
400| |10|1
2
3|302
311
320|335
369
398|196
235
265|372
381
391|429
473
511|252
302
339|506
517
528|534
589
637|308
368
413| |15|1
2
3|312
321
331|380
411
438|208
248
281|397
407
418|482
522
557|266
317
360|556
568
579|596
646
690|324
387
437| |20|1
2
3|306
317
326|425
453
476|217
259
294|390
400
412|538
574
607|276
331
375|546
558
570|664
709
750|336
403
457| |30|1
2
3|296
307
316|497
521
542|230
274
309|378
389
400|630
662
690|294
349
394|528
541
555|779
819
855|358
425
482| |50|1
2CMC § 1.1.4 Medium relevance — show source text
see Notes 2, 18, 26, 34, 40;
facings: side 1; see Note 38.|80 psi|5 hrs||1||1, 20|5| |W-8-M-91|81/2″|Cored concrete masonry; see Notes 2, 19, 26, 31, 40;
facings: fire side only; see Note 38.|80 psi|1 hr
45 min||1||1, 20|13/4| |W-8-M-92|81/2″|Cored concrete masonry; see Notes 2, 18, 26, 31, 40;
facings: one side; see Note 38.|80 psi|4 hrs||1||1, 20|4|2025 CALIFORNIA EXISTING BUILDING CODE RESOURCE A-37
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
RESOURCE A—GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS AND ASSEMBLIES
TABLE 1.1.4—continued
MASONRY WALLS
8″ TO LESS THAN 10″ THICKCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 ITEM CODE THICKNESS CONSTRUCTION DETAILS PERFORMANCE PERFORMANCE REFERENCE NUMBER REFERENCE NUMBER REFERENCE NUMBER NOTES REC.
HOURSITEM CODE THICKNESS CONSTRUCTION DETAILS LOAD TIME PRE-
BMS-92BMS-92 POST-
BMS-92POST-
BMS-92POST-
BMS-92W-8-M-93 81/2″ Cored concrete masonry; see Notes 2, 19, 26, 36, 41;
facings: fire side only; see Note 38.80 psi 2 hrs 1 1, 20 2 W-8-M-94 81/2″ Cored concrete masonry; see Notes 2, 18, 26, 36, 41;
facings: fire side only; see Note 38.80 psi 4 hrs 1 1, 20 4 W-8-M-95 81/2″ Cored concrete masonry; see Notes 2, 19, 26, 34, 41;
facings: fire side only; see Note 38.80 psi 1 hr
30
min1 1, 20 11/2 W-8-M-96 81/2″ Cored concrete masonry; see Notes 2, 18, 26, 34, 41;
facings: one side; see Note 38.80 psi 3 hrs 1, 20 3 W-8-M-97 81/2″ Cored concrete masonry; see Notes 2, 19, 26, 29, 41;
facings: fire side only; see Note 38.CMC § 403.7.2.3 Medium 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 hoods4 Kitchen hoods other than grease 3
Diazo printing equipment discharge4
Hydraulic elevator machine room2
Laboratory hoods4 Paint spray booths 4 Refrigerating machinery rooms3403.9.1 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 Medium 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
74 2025 CALIFORNIA MECHANICAL CODE
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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 § 160.2 Medium 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 § 120.1 Medium relevance — show source text
**
- 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.
- 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.
- 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.
- 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]
2025 CALIFORNIA ENERGY CODE 71
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS
- Class 2 Air is air with moderate contaminant concentration, mild sensory-irritation intensity or mildly offensive odors (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 120.1(g)2A through 120.1(g)2E: A. Recirculation of Class 2 air within the space of origin shall be permitted [ASHRAE 62.1:5.13.3.2.1]; B. Recirculation or transfer of Class 2 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 C. Transfer of Class 2 air to toilet rooms [ASHRAE 62.1:5.13.3.2.3]; or
D. Recirculation or transfer of Class 2 air to Class 4 spaces [ASHRAE 62.1:5.13.3.2.4]; or E. Class 2 air shall not be recirculated or transferred to Class 1 spaces. [ASHRAE 62.1:5.13.3.2.5] Exception to Section 120.1(g)2E: When using any energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device is permitted.
CMC § 90.1 Medium 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.
2025 CALIFORNIA MECHANICAL CODE 437
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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 § 31F-3 Medium relevance — show source text
|Note:Linear interpolation can he used to estimate values of Fa for intermediate values of SS.
* Site-specific dynamic site response analysis shall be performed.|Note:Linear interpolation can he used to estimate values of Fa for intermediate values of SS.
* Site-specific dynamic site response analysis shall be performed.|Note:Linear interpolation can he used to estimate values of Fa for intermediate values of SS.
* Site-specific dynamic site response analysis shall be performed._|TABLE 31F-3-4—VALUES OF F
vCol2 Col3 Col4 Col5 Col6 SITE CLASS S1 S1 S1 S1 S1 SITE CLASS < 0.1 0.2 0.3 0.4 > 0.5 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.7 1.6 1.5 1.4 1.3 D 2.4 2.0 1.8 1.6 1.5 E 3.5 3.2 2.8 2.4 2.4 F * * * * * Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.Note:Linear interpolation can he used to estimate values of Fv for intermediate values of S1.
* Site-specific dynamic site response analysis shall be performed.3103F.4.2.5 Site-specific evaluation of amplification effects. As an alternative to the procedure presented in Section 3103F.4.2.4, a site-specific response analysis may be performed. For Site Class F a site-specific response analysis is required. The analysis shall be either an equivalent linear or nonlinear analysis. Appropriate acceleration time histories as discussed in Section 3103F.4.2.10 shall be used.
CMC § 160.2 Medium 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 § 120.1 Medium 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:
Within 5 feet of the unit; or
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.
- 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.
- 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.
- 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.
- 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]
2025 CALIFORNIA ENERGY CODE 71
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
CMC § 140.4 Medium relevance — show source text
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|SZHP = Single Zone Heat Pump + Economizer in accordance with Section 140.4(e).
SZAC1 = Single Zone Air Conditioner with furnace + Variable Speed Fan, + Economizer in accordance with Section 140.4(e), or Dual Fuel Heat Pump + Variable Speed Fan +
Economizer in accordance with Section 140.4(e).
NR = No Requirement.|Air conditioners with furnaces or dual fuel heat pumps complying with Table 141.0-E-1 using variable speed fan and controls shall be designed to vary the indoor fan airflow rate as a function of the load and shall have a minimum of two stages of fan control. The minimum speed at stage 1 shall be set for ventilation only mode and shall be the greater of 50 percent or the minimum fan speed required to meet the minimum ventilation airflow rate. The indoor fan shall draw not more than 30 percent of the fan power at full fan speed when operating at 50 percent speed. Exception to Section 141.0(b)2Cii: Section 141.0(b)2Cii is not applicable if the alteration exceeds the existing main service panel or service transformer capacity. An electrical load calculation shall be submitted by a registered professional engineer in accordance with Article 220 of the California Electrical Code .
CMC § 909.12 Medium relevance — show source text
864—2014: Control Units and Accessories for Fire Alarm Systems as amended* —with Revisions through May 2020
909.12
*Amend No. 55.1 as follows:
RETARD-RESET-RESTART PERIOD – MAXIMUM 30 SECONDS —No alarm obtained from control unit. Maximum permissible time is 30 seconds.
*Amend Section 55.2.2 as follows:
Where an alarm verification feature is provided, the maximum retard-reset-restart period before an alarm signal can be confirmed and indicated at the control unit, including any control unit reset time and the power-up time for the detector to become operational for alarm, shall not exceed 30 seconds. (The balance of the section text is to remain unchanged).
*Add Section 55.2.9 as follows:
Smoke detectors connected to an alarm verification feature shall not be used as releasing devices.
Exception: Smoke detectors which operate their releasing function immediately upon alarm actuation independent of alarm verification feature.
*Amend Section 89.1.10 as follows:
The existing text of this section is to remain as printed with one editorial amendment as follows:
THE TOTAL DELAY (CONTROL UNIT PLUS SMOKE DETECTORS) SHALL NOT EXCEED 30 SECONDS.
(The balance of the section text is to remain unchanged).
924—2016: Emergency Lighting and Power Equipment—with Revisions through May 2020
1013.5
2025 CALIFORNIA BUILDING CODE 35-43
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
REFERENCED STANDARDS
1034-2011: Burglary-Resistant Electric Locking Mechanisms—with Revisions through June 2020
1010.2.10, 1010.2.11, 1010.2.12.1, 1010.2.13, 1010.2.14
1040—1996: Fire Test of Insulated Wall Construction—with Revisions through April 2017
1406.10.2, 2603.9
1256—2002: Fire Test of Roof Deck Construction—with Revisions through August 2018
1508.1, 2603.3, 2603.4.1.5
1479—2015: Fire Tests of Penetration Firestops—with Revisions through May 2021
202, 714.4.1.2, 714.4.2, 714.5.1.2, 714.5.4
1482—2011: Solid-fuel Type Room Heaters—with Revisions through February 2020
2112.2, 2112.5
1489—2016: Fire Tests of Fire Resistant Pipe Protection Systems Carrying Combustible Liquids—with Revisions through October
2021
403.4.8.2
1703—2002: Flat-plate Photovoltaic Modules and Panels—with Revisions through November 2019
1507.17.5, 3111.3.1
1715—1997: Fire Test of Interior Finish Material—with Revisions through April 2017
1406.10.2, 2603.9, 2614.4
1741—2010: Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources—with Revisions through June 2021
Frequently asked questions
Can I always average occupancy for design?
Yes — when the peak occupancy is short or occupancy fluctuates, § 403.6.1 permits averaging the zone population (Pz) over the code‑computed averaging time T. But you must compute T from the zone volume (v) and Vbz and ensure the delivered average outdoor air over T meets the breathing‑zone requirement.
Does dynamic reset let me reduce outdoor air permanently?
No — § 403.8 permits resetting Vot and/or Voz as conditions change, but the system must still meet the breathing‑zone minimums when the space is occupied. Part‑load reductions are allowed, but design must ensure compliance during occupied periods (and averaging rules apply when used).
How do I pick the averaging time T in practice?
Use the code formula T = 3·v / Vbz in § 403.6.1 (minutes). Compute the zone volume and the breathing‑zone outdoor airflow (Vbz) per § 403.2.1, then plug into the formula.
If I intermittently close the outdoor‑air damper, what must I show?
You must show that the average outdoor‑air intake over the averaging time T is not less than the minimum outdoor-air intake (Vot) determined for the system (per § 403.6.1).
Where does the code say I can reset zone airflow?
The permission to design systems that reset Vot and/or Voz as operating conditions change is explicitly given in § 403.8. The code does not mandate a particular reset control logic.
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