Chapter 4 — VENTILATION AIR

(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.)

• [>]

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.

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

68 2025 CALIFORNIA MECHANICAL CODE

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

CHAPTER 4

VENTILATION AIR

ventilation air supply, exhaust, and makeup air requirements for occupiable spaces within a building. [OSHPD 1, 1R, 2, 3, 4 & 5] See Sections 406.0 through 419.0. [SFM] Air filters shall comply with all requirements of Part 12, Title 24, Chap- ter 12-71, SFM Standard 12-71-1. Spaces within buildings, except those within a dwelling unit in residential occupancies where occupants are nontransient, shall comply with Section 402.0 through Section 404.0. Requirements for ventilation air rate for dwelling units in residential occupancies, where the occupants are nontransient, shall be in accordance with Section 405.0 or ASHRAE 62.2.

systems serving an indoor aquatic facility (natatorium) shall comply with the Uniform Swimming Pool, Spa and Hot Tub Code (USPSHTC).

tilated buildings, provide regularly occupied areas of the building with air filtration media for outside and return air that provides at least a Minimum Efficiency Reporting Value (MERV) of 13. MERV 13 filters shall be installed prior to occupancy, and recommendations for maintenance with fil- ters of the same value shall be included in the operation and maintenance manual in compliance with Chapter 5, Division 5.5 of the California Green Building Standards Code (CAL- Green).

Exception: Existing mechanical equipment.

401.3.1 Labeling. Installed filters shall be clearly labeled by the manufacturer indicating the MERV rating.

Table 402.1 shall be designed to have ventilation (outdoor) air for occupants in accordance with this chapter. [DSA-SS] Ven- tilation air requirements for occupancies regulated by the California Energy Commission are found in the California Energy Code.

[CEC] Ventilation air requirements for occupancies regu- lated by the California Energy Commission and found in the California Energy Code supersede those of the California Mechanical Code.

[OSHPD 1, 2, 3, 4 & 5] Health care spaces shall meet the ventilation requirements found in Table 4-A. Ventilation rates for areas not specified in Table 4-A shall have minimum ven- tilation and air change rates per ANSI/ASHRAE Standard 62.1. Where areas with prescribed ventilation rates in both Standards 62.1 and Table 4-A exist, the higher of the two air change rates shall be used.

402.1.1 Construction Documents. The outdoor air ventilation rate and air distribution assumptions made in the design of the ventilation system shall be clearly identified on the construction documents.

402.1.2 Ventilation in Health Care Facilities.

Mechanical ventilation for health care facilities shall be designed and installed in accordance with this code, ASHRAE/ASHE 170, and NFPA 99. [OSHPD 1, 1R, 2, 3, 4 & 5] Ventilation for health care facilities shall be designed and installed in accordance with this code and Table 4-A. All supply-air, return air, and exhaust-air sys- tems shall comply with this code and ASHRAE 170. When the requirements of this code conflict with ASHRAE 170, the most restrictive requirements shall prevail. The text of ASHRAE 170 shall be modified as follows:

(1) ASHRAE 170. Section 6.1.2.1 -- Also see Section 319.0.

(2) ASHRAE 170. Section 6.3.1.3 – Modify as follows: Relief air other than class 1 shall discharge at least 10 feet (3048 mm) from any outside air intake.

(3) ASHRAE 170. Section 6.3.2 -- Also see Section 407.1.2 and 407.2.2.

(4) ASHRAE 170. Section 6.4 -- Modify as follows:

c.: Replace Table 7-1, 8-1, 8-2, or 9-1 with Table 4-A.

d.: Replace Table 7-1, 8-1, 8-2, or 9-1 with Table 4-A.

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

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

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

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

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

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

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

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

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

Delete the Exception that allows for high return grilles.

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

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

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

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

VENTILATION AIR

«

«

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

[ASHRAE 62.1:6.4.1.5]

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

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

402.2.1.6(A) Sizing Openings. Where the zone is ventilated using a single opening or multiple single openings located at the same elevation, the openable area as a percent of the net occupiable floor area shall be greater than or equal to the value indicated in Table 402.2.1.6(A)(1). Where the zone is ventilated using two openings located at different elevations or multiple pairs of such openings, the openable area as a percent of the net occupiable floor area shall be greater than or equal to the value indicated in Table 402.2.1.6(A)(2).

Where openings are obstructed by louvers or screens, the openable area shall be based on the net free area of the opening. Where interior zones, or portions of zones, without direct openings to the outdoors are ventilated through adjoining zones, the opening between zones shall be permanently unobstructed and have a free area of not less than twice the percent of occupiable floor area used to determine the opening size of adjacent exterior zones, or 25 square feet (2.3 m [2] ), whichever is greater. Table 402.2.1.6(A)(1) and Table 402.2.1.6(A)(2) are based on buoyancy-driven flow and shall not address thermal comfort. [ASHRAE 62.1:6.4.1.6.1]

402.2.2 Engineered System Compliance Path. For an engineered natural ventilation system, the following shall be included:

(1) Determine hourly environmental conditions, including outdoor air dry-bulb temperature; dew-point temperature; outdoor concentration of contaminants, including PM2.5, PM10, and ozone where data are available; wind speed and direction; and internal heat gains during expected hours of natural ventilation operation.

»

»

»

»

for OSHPD 1, 2, 3, 4 & 5] Natural ventilation systems shall comply with the requirements of either Section 402.2.1 through Section 402.2.1.6(A) or Section 402.2.2. Designers shall provide interior air barriers, insulation, or other means that separate naturally ventilated spaces from mechanically cooled spaces to prevent high-dew-point outdoor air from coming into contact with mechanically cooled surfaces.

[ASHRAE 62.1:6.4]

402.2.1 Prescriptive Compliance Path. Any zone designed for natural ventilation shall include a mechanical ventilation system designed in accordance with Section 403.0.

Exceptions:

(1) Zones in buildings that have all of the following:

(a) Natural ventilation openings that comply with the requirements of Section 402.2.1.

(b) Controls that prevent the natural ventilation openings from being closed during periods of expected occupancy, or natural ventilation openings that are permanently open.

(2) Zones that are not served by heating or cooling equipment. {ASHRAE 62.1:6.4.1}

402.2.1.1 Ceiling Height. For ceilings that are parallel to the floor, the ceiling height ( H ) to be used in Section 402.2.1.3 through Section 402.2.1.5 shall be the minimum ceiling height in the zone.

For zones where ceiling height increases as distance from the openings is increased, the ceiling height shall be determined as the average height of the ceiling within 20 feet (6096 mm) from the operable openings. [ASHRAE 62.1:6.4.1.1]

402.2.1.2 Floor Area to be Ventilated. The nat urally ventilated area in zones or portions of zones shall extend from the openings to a distance determined in accordance with Section 402.2.1.3, Section 402.2.1.4, or Section 402.2.1.5. Openings shall be in accordance with the requirements of Section 402.2.1.6.

For zones where ceilings are not parallel to the floor, the ceiling height shall be determined in accordance with Section 402.2.1.1. [ASHRAE 62.1:6.4.1.2]

402.2.1.3 Single Side Opening. For zones with openings on only one side of the zone, the naturally ventilated area shall extend to a distance not greater than 2 times the height of the ceiling from the openings. [ASHRAE 62.1:6.4.1.3]

402.2.1.4 Double Side Opening. For zones with openings on two opposite sides of the zone, the naturally ventilated area shall extend between the openings separated by a distance not greater than 5 times the height of the ceiling. [ASHRAE 62.1:6.4.1.4]

70 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 402.2.1.6(A)(1) MINIMUM OPENABLE AREAS: SINGLE OPENINGS*

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]

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

For SI unit: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 square foot = 0.0929 m [2], 1 foot = 304.8 mm,

Where:

Vbz = breathing zone outdoor airflow, per Table 402.1. Az = zone floor area, the net occupiable floor area of the ventilation zone. Hvs = vertical separation between the center of the top and bottom openings’ free operable area; in case of multiple horizontally spaced pairs of openings, use shortest distance encountered. As = openable area of smallest opening (top or bottom); in case of multiple horizontally spaced pairs of top-and-bottom openings, use aggregated areas. Al = openable area of largest opening (top or bottom); in case of multiple horizontally spaced pairs of top-and-bottom openings, use aggregated areas.

• Volumetric airflow rates used to estimate required operable 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

ical ventilation systems shall include controls, manual or automatic, that enable the fan system to operate wherever the spaces served are occupied. The system shall be designed to maintain minimum outdoor airflow as required by Section 403.0 under any load conditions.

air intakes shall be designed in accordance with Section 402.4.1 through Section 402.4.5. [ASHRAE 62.1:5.5]

402.4.1 Location. Outdoor air intakes (including openings that are required as part of a natural ventilation system) shall be located such that the shortest distance from the intake to any specific potential outdoor contaminant source listed in Table 402.4.1 shall be equal to or greater than the following:

(1) The separation distance in Table 402.4.1 or

(2) The calculation methods in ASHRAE 62.1 Normative Appendix B and shall comply with all other requirements of this section. [ASHRAE 62.1:5.5.1]

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

VENTILATION AIR

TABLE 402.4.1

AIR INTAKE MINIMUM SEPARATION DISTANCE

[ASHRAE 62.1:TABLE 5-1]

For SI units: 1 foot = 304.8 mm

402.4.1.1 Exhaust/Relief Outlets. Separation criteria for Class 2 and Class 3 exhaust/relief outlets apply to the distance from the outdoor air intakes for one ventilation system to the exhaust and relief outlets for any other ventilation system. [ASHRAE 62.1:5.5.1.1]

402.4.1.2 Fuel-Burning Equipment. The minimum distances relative to fuel-fired appliances shall be as required by NFPA 54/ANSI Z223.1 for fuelgas-burning appliances and equipment, NFPA 31 for oil burning appliances and equipment, and NFPA 211 for other combustion appliances and equipment.

[ASHRAE 62.1:5.5.1.2]

402.4.1.3 Roof, Landscaped Grade, or Another Surface Directly Below Intake. Where snow accumulation is expected, the surface of the snow at the expected average snow depth shall be considered to be a surface directly below an intake.

Exception: The minimum separation distance in Table 402.4.1 shall not apply where outdoor surfaces below the air intake are sloped more than 45 degrees (0.79 rad) from horizontal or where such surfaces are less than 1 inch (25.4 mm) in width.

[ASHRAE 62.1:5.5.1.3]

402.4.1.4 Laboratory Exhaust. Separation criteria for fume hood exhaust shall be in compliance with ANSI/ASSP Z9.5. [ASHRAE 62.1:5.5.1.4]

402.4.2 Rain Entrainment. Outdoor air intakes that are part of the mechanical ventilation system shall be designed to manage rain entrainment in accordance with one or more of the following:

(1) Limit water penetration through the intake to 0.07 oz/(ft [2] - h) [21.5 g/(m [2] - h)] of inlet area when tested using the rain test apparatus described in UL 1995.

(2) Select louvers that limit water penetration to a maximum of 0.01 oz/ft [2] (3.05 g/m [2] ) of louver free area at the maximum free area intake velocity through the louver. This water penetration rate shall be determined when subjected to the water penetration test in AMCA 500-L or equivalent. Manage the water that penetrates the louver by providing a drainage area or moisture removal devices.

(3) Select louvers that are Class A when rated according to AMCA 511 and tested per the AMCA 500-L wind-driven rain test when subjected to a simulated rainfall of 3 inches (76 mm) per hour and a 29 mph (13 m/s) wind velocity. The maximum design core area velocity through the louver shall correlate to a Class A rating.

(4) Use rain hoods sized for no more than 500 feet per minute (2.5 m/s) face velocity with a downward-facing intake such that all intake air passes upward through a horizontal plane that intersects the solid surfaces of the hood before entering the system.

(5) Manage the water that penetrates the intake opening by providing a drainage area or moisture removal devices. {ASHRAE 62.1:5.5.2} 402.4.3 Rain Intrusion. Air-handling and distribution equipment mounted outdoors shall be designed to prevent rain intrusion into the airstream when tested at design airflow and with no airflow, using the rain test apparatus described in UL 1995. [ASHRAE 62.1:5.5.3] 402.4.4 Snow Entrainment. Where climate dictates, outdoor air intakes that are part of the mechanical ventilation system shall be designed as follows to manage water from snow that is blown or drawn into the system:

(1) Access doors to permit cleaning of wetted surfaces shall be provided.

(2) Outdoor air ductwork or plenums shall pitch to drains designed in accordance with the requirements of ASHRAE 62.1. [ASHRAE 62.1:5.5.4]

402.4.5 Bird Screens. Outdoor air intakes shall include a screening device designed to prevent penetration by a 0.5 inch (13 mm) diameter probe. The screening device material shall be corrosion resistant. The screening device shall be located, or other measures shall be taken, to prevent bird nesting within the outdoor air intake. [ASHRAE 62.1:5.5.5]

2, 3, 4 & 5 spaces listed in Table 4-A]

a ventilation system shall be determined in accordance with Section 403.2 through Section 403.10.

72 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

shall be determined in accordance with Section 403.2.1 through Section 403.2.3 for ventilation zones served by the ventilation system, except that the ventilation rates from ASHRAE/ASHE 170 shall be used for the occupancy categories, as applicable. [ASHRAE 62.1:6.2.1]

403.2.1 Breathing Zone Outdoor Airflow. The outdoor airflow required in the breathing zone ( Vbz ) of the occupiable space or spaces in a ventilation zone shall be not less than the value determined in accordance with Equation 403.2.1.

Vbz = Rp•Pz + Ra• Az (Equation 403.2.1)

Where: Az = zone floor area, the net occupiable floor area of the ventilation zone, ft [2] (m [2] ). Pz = zone population, the number of people in the ventilation zone during usage. Rp= outdoor airflow rate required per person (CFM/person) as determined from Table 402.1. Ra= outdoor airflow rate required per unit area (CFM/ft [2] ) as determined from Table 402.1.

[ASHRAE 62.1:6.2.1.1] For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ] 403.2.2 Zone Air Distribution Effectiveness. The zone air distribution effectiveness ( Ez ) shall be determined in accordance with Table 403.2.2. [ASHRAE 62.1:6.2.1.2] 403.2.2.1 Stratified Air Distribution Systems. A stratified air distribution system shall be designed in accordance with Section 403.2.2.1.1 through Section 403.2.2.2.2, or the zone air distribution effectiveness ( Ez ) shall be determined in accordance with ASHRAE 62.1. [ASHRAE 62.1:6.2.1.2.1] 403.2.2.1.1 Supply Air. Cool air shall be at least 4°F (2°C) less than the average room air temperature. [ASHRAE 62.1:6.2.1.2.1.1] 403.2.2.1.2 Return Air. The return air openings or pathways shall be located not less than 9 feet (2743 mm) above the floor. [ASHRAE 62.1:6.2.1.2.1.2]

403.2.2.1.3 Stratification. The zone shall not contain any devices that mechanically mix the air, and shall be protected from impinging airstreams from adjacent ventilation zones.

[ASHRAE 62.1:6.2.1.2.1.3] 403.2.2.2 Personalized Ventilation Systems. A personalized ventilation system shall be designed in accordance with the following subsections, or the zone air distribution effectiveness ( Ez ) shall be determined in accordance with ASHRAE 62.1.

[ASHRAE 62.1:6.2.1.2.2] 403.2.2.2.1 Personalized Air. The personalized air shall be distributed in the breathing zone and designed such that the velocity is

equal to or less than 50 feet per minute (0.25 m/s) at the head/facial region of the occupant.

[ASHRAE 62.1:6.2.1.2.2.1] 403.2.2.2.2 Return Air. The return air openings or pathways shall be located more than 9 feet (2.8 m) above the floor. [ASHRAE 62.1:6.2.1.2.2.2]

403.2.3 Zone Outdoor Airflow. The zone outdoor airflow ( Voz ) provided to the ventilation zone by the supply air distribution system shall be determined in accordance with Equation 403.2.3. [ASHRAE 62.1:6.2.1.3]

Voz = Vbz / Ez (Equation 403.2.3)

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)

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)

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.

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

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)

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.

[ASHRAE 62.1:6.2.5.2]

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

74 2025 CALIFORNIA MECHANICAL CODE

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

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.

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]

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]

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

403.9.2 Class 2 Air. Recirculation of Class 2 air within the space of origin shall be permitted. 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. Transfer of Class 2 air to toilet rooms shall be permitted. Recirculation or transfer of Class 2 air to Class 4 spaces shall be permitted. Class 2 air shall not be recirculated or transferred to Class 1 spaces.

Exception: When using any energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device shall be permitted but shall not be counted as outdoor air. Exhaust air transfer ratio of Class 2 air shall not exceed 10 percent of the outdoor air intake flow. {ASHRAE 62.1:5.18.3.2 – 5.18.3.2.5}

403.9.3 Class 3 Air. Recirculation of Class 3 air within the space of origin shall be permitted. Class 3 air shall not be recirculated or transferred to any other space.

Exception: When using any energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device shall be permitted but shall not be counted as outdoor air. Exhaust air transfer ratio of Class 3 air shall not exceed 5 percent of the outdoor air intake flow. {ASHRAE 62.1:5.18.3.3 – 5.18.3.3.2}

403.9.4 Class 4 Air. Class 4 air shall not be recirculated or transferred to any space or recirculated within the space of origin. [ASHRAE 62.1:5.18.3.4]

shall be tested, balanced, and operated to demonstrate that the installation and performance of the systems are in accordance with the design intent. All testing and balancing shall be performed by a technician certified by the Associated Air Balance Council (AABC), the National Environmental Balancing Bureau (NEBB), the Testing, Adjusting and Balancing Bureau (TABB), or other equivalent approved agencies.

Exception: For single family residential, compliance with Section 403.10 shall not be required.

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

VENTILATION AIR

tems Ventilation Efficiency.

The system ventilation efficiency shall equal the lowest zone ventilation efficiency among the ventilation zones served by the air handler in accordance with Equation 404.1. [ASHRAE 62.1:A1.3] This section presents an alternative procedure for calculating the system ventilation efficiency ( Ev ) for multiple zone recirculating systems that shall be used when Section 403.5.1.3 is not used.

Ev = minimum ( Evz ) (Equation 404.1)

The average outdoor air fraction ( X s) for the ventilation system shall be determined in accordance with Equation 404.2.

Xs =Vou / Vps (Equation 404.2)

Where the uncorrected outdoor air intake ( Vou ) is determined in accordance with Section 403.5.1, and the system primary airflow ( Vps ) shall be determined at the condition analyzed. [ASHRAE 62.1:A1.1]

efficiency ( Evz ) shall be determined in accordance with Section 404.3.1 or Section 404.3.2. [ASHRAE 62.1:A1.2] 404.3.1 Single Supply Systems. For single supply systems, where all of the air supplied to each ventilation zone is a mixture of outdoor air and system-level recirculated air, zone ventilation efficiency ( Evz ) shall be determined in accordance with Equation 404.3.1(1). Examples of single supply systems include constant-volume reheat, single-duct VAV, single-fan dual-duct, and multizone-systems.

Evz = 1+ Xs – Zpz [Equation 404.3.1(1)]

Where the average outdoor air fraction for the system ( Xs ) shall be determined in accordance with Equation 404.2 and the primary outdoor air fraction for the zone ( Zpz ) shall be determined in accordance with Equation 404.3.1(2).

Zpz = Voz/Vpz [Equation 404.3.1(2)]

For VAV systems, Vpz is the lowest zone primary airflow value expected at the design condition analyzed.

[ASHRAE 62.1:A1.2.1] 404.3.2 Secondary-Recirculation Systems. For secondary-recirculation systems where the supply air or a portion thereof to each ventilation zone is recirculated air (air that has not been directly mixed with outdoor air) from other zones, zone ventilation efficiency ( Evz ) shall be determined in accordance with Equation 404.3.2(1). Examples

of secondary-recirculation systems include dual-fan dualduct and fan-powered mixing-box systems, and systems that include transfer fans for conference rooms.

[Equation 404.3.2(1)] Evz = ( Fa+Xs•Fb–Zpz•Ep•Fc )/ Fa

Where system air fractions Fa, Fb, and Fc are determined in accordance with Equation 404.3.2(2), Equation 404.3.2(3), and Equation 404.3.2(4), as applicable.

Fa = Ep + (1– Ep )• Er [Equation 404.3.2(2)]

Fb = Ep [Equation 404.3.2(3)]

Fc = 1–(1– Ez )•(1– Er )•(1– Ep ) [Equation 404.3.2(4)]

Where the zone primary air fraction ( Ep ) shall be determined in accordance with Equation 404.3.2(5), zone secondary recirculation fraction ( Er ) shall be determined by the designer based on system configuration, and zone air distribution effectiveness ( Ez ) shall be determined in accordance with Section 403.2.2. [ASHRAE 62.1:A1.2.2]

Ep = Vpz / Vdz [Equation 404.3.2(5)]

Where:

Az = Zone floor area: The net occupiable floor area of the ventilation zone, ft [2] (m [2] ).

D = Occupant diversity: The ratio of the system population to the sum of the zone populations. Ep = Primary air fraction: The fraction of primary air in the discharge air to the ventilation zone. Er = Secondary recirculation fraction: In systems with secondary recirculation of return air, the fraction of secondary recirculated air to the zone that is representative of average system return air rather than air directly recirculated from the zone. Ev = System ventilation efficiency: the efficiency with which the system distributes air from the outdoor air intake to the breathing zone in the ventilationcritical zone, which requires the largest fraction of outdoor air in the primary airstream. Evz = Zone ventilation efficiency: The efficiency with which the system distributes air from the outdoor air intake to the breathing zone in any particular ventilation zone.

Ez = Zone air distribution effectiveness: A measure of the effectiveness of supply air distribution to the breathing zone. Ez is determined in accordance with Section 403.2.2.

Fa = Supply air fraction: The fraction of supply air to the ventilation zone from sources or air outside the

zone.

76 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

Fb = Mixed air fraction: The fraction of supply air to the ventilation zone from fully mixed primary air.

Fc = Outdoor air fraction: The fraction of outdoor air to the ventilation zone from sources of air outside

the zone.

Ps = System population: the simultaneous number of occupants in the area served by the ventilation sys tem.

Pz = Zone population: see Section 403.2.1. Ra = Area outdoor air rate, CFM/ft [2] . See Section 403.2.1.

Rp = People outdoor air rate, CFM/person. See Section 403.2.1.

Vbz = Breathing zone outdoor airflow, CFM. See Section 403.2.1.

Vdz = Zone discharge airflow, CFM. The expected discharge (supply) airflow to the zone that includes primary airflow and secondary recirculated airflow, CFM.

Vot = Outdoor air intake flow, CFM. See Section 403.3, Section 403.4, and Section 403.5.2.

Vou = Uncorrected outdoor air intake, CFM. See Section 403.5.1.

Voz = Zone outdoor airflow, CFM. See Section 403.2.3. Vps = System primary airflow, CFM. The total primary airflow supplied to all zones served by the system from the air-handling unit at which the outdoor air intake is located.

Vpz = Zone primary airflow, CFM. The zone primary airflow to the ventilation zone, including outdoor air and recirculated air.

Xs = Average outdoor air fraction: At the primary air handler, the fraction of outdoor air intake flow in the system primary airflow. Zpz = Primary outdoor air fraction: The outdoor air fraction required in the primary air supplied to the ventilation zone prior to the introduction of any secondary recirculation air. [ASHRAE 62.1:A3]

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

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

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

Rooms or occupied spaces within residential occupancies, where the occupants are nontransient, shall be designed to have mechanical ventilation and exhaust air in accordance with Section 405.2 through Section 405.5.

405.1.1 Natural Ventilation. Where approved by the Authority Having Jurisdiction, natural ventilation shall be permitted for Climate Zone 1, Climate Zone 2, or for thermally conditioned buildings for less than 876 hours

per year.

The required mechanical ventilation outdoor air rate ( Qtot ) shall be as calculated in accordance with Equation 405.2.

Exception: For existing buildings and where permitted by the Authority Having Jurisdiction, the total mechanical ventilation ( Qtot ) is not required where Qtot is calculated to be less than 15 ft [3] /min (7.08 L/s).

Qtot = 0.03 Afloor + 7.5 ( Nbr + 1) (Equation 405.2)

Where:

Qtot = Total required ventilation outdoor air rate, CFM (L/s) Afloor = Floor area, ft [2] (m [2] ) Nbr = Number of bedrooms more than 1

For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s

405.2.1 Reduced Ventilation Air Rate. Where permitted by the Authority Having Jurisdiction, the mechanical ventilation air rate required in Section 405.2 shall be permitted to be reduced where an infiltration rate is determined in accordance with ASTM E779.

to the outdoors shall be provided in each room containing a bathtub, shower, or tub/shower combination. The fan shall run intermittently (on demand) or continuously. A readily accessible manual control designed to be operated as needed or an automatic control shall be provided for intermittent operations. [HCD 1 & HCD 2] Each bathroom shall also be mechanically ventilated in accordance with Division 4.5 of the California Green Building Standards Code (CALGreen).

405.3.1 Exhaust Rate. The exhaust rate shall be not less than 50 ft [3] /min (23.6 L/s) for intermittent operation and 25 ft [3] /min (11.8 L/s) for continuous operation.

discharges directly to the outdoors shall be provided in each kitchen. The fan shall run intermittently (on demand) or continuously. A readily accessible manual control designed to be operated as needed or an automatic control shall be provided for intermittent operations.

Exception: Recirculating systems installed in accordance with Section 516.0 and the manufacturer’s installation

instructions.

405.4.1 Exhaust Rate. For intermittent-controlled operations, the exhaust rate shall be not less than 100 ft [3] /min (47.2 L/s) for range hoods or 300 ft [3] /min (142 L/s) for mechanical exhaust fans including downdraft appliances. For continuous operated ventilation, the exhaust rate shall be not less than 50 ft [3] /min (23.6 L/s).

provided with a readily accessible ventilation opening openable to the outdoors. The opening shall be not less than 5 square feet (0.464 m [2] ) or 4 percent of the occupied floor area. The openable area shall be based on free, unobstructed area through the opening.

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

VENTILATION AIR

Facilities. [OSHPD 1, 2, 3, 4 & 5] Direct evaporative cool- ing systems where the air directly contacts the wetted surface or spray shall be limited in health facilities to nonpatient areas such as laundry rooms, and boiler or machinery rooms. Similar rooms with high heating-producing equipment will be consid- ered when specifically approved by the enforcing agency. The evaporative pads shall be a synthetic type. Filters shall be required in accordance with Tables 4-B and 4-C except utility rooms, i.e.: boiler or machinery rooms.

& 5]

407.1.1 All supply-air, return air, and exhaust-air sys- tems shall be mechanically operated and such systems for areas listed in Table 4-A shall be operated continu- ously. Natural ventilation through windows or other openings such as louvers will be considered as supple- mental to the required mechanical ventilation systems.

Exceptions:

(1) Natural ventilation shall not be used in airborne infection isolation rooms and protective environment

rooms.

(2) Unoccupied turndown shall be permitted in accor- dance with Section 407.7.

407.1.2 Fans serving exhaust systems shall be located at the discharge end of the system. Ductwork within the building shall be under negative pressure. The ventilation rates shown in Table 4-A shall be considered as minimum acceptable rates and shall not be construed as precluding the use of higher ventilation rates if they are required to meet design conditions. 407.1.3 Services/Systems and Utilities. (Refer to Sec- tion 1224.4.1 of the California Building Code).

407.2.1 Outdoor Air Intakes. Outdoor air intakes shall be located at least 25 feet (7.62 m) from exhaust outlets of ventilating systems, combustion equipment stacks, med- ical-surgical vacuum systems, cooling towers, and areas that may collect vehicular exhaust or other noxious fumes. Plumbing vents shall be located in relation to out- door air intakes per California Plumbing Code. The bot- tom of outdoor air intakes shall be located as high as practicable, but not less than 10 feet (3048 mm) above ground level. If installed above the roof, they shall be located 18 inches (457 mm) above roof level or 3 feet (914 mm) above a flat roof where heavy snowfall is anticipated. Outside air intakes located in a below grade areaway shall have the top of the areaway extend a minimum of 10 feet (3048 mm) above grade.

Exceptions:

(1) These dimensions may be reduced if it is demon- strated by the submission of details and calculations that location of intakes with respect to exhausts and

their orientation, or the use of special filters, pro- vides equal performance.

(2) The requirements regarding the bottom of outdoor air intakes and installation through the roof do not apply to skilled nursing facilities, intermediate-care facilities or nonsensitive areas in correctional treat-

ment centers.

407.2.2 Exhaust Outlets. Exhaust outlets shall be located a minimum of 10 feet (3048 mm) above adjoining grade and 10 feet (3048 mm) from doors, occupied areas, and operable windows.

Exception: Airborne infection isolation rooms shall comply with Section 414.1.

407.2.2.1 Hazardous Exhaust Outlets. Haz- ardous exhaust outlets from airborne infection iso- lation rooms, bronchoscopy and sputum collection exhaust, hazardous drug compounding, morgues, autopsy rooms and laboratory chemical fume hoods shall discharge a minimum of 10 feet (3048 mm) above the adjacent roof surface and a minimum of 30 feet (9144.mm) from outdoor air intakes, build- ing openings and areas normally accessible to the public.

407.3.1 The ventilation systems shall be designed and balanced to provide the general air balance relationship to adjacent areas, shown in Table 4-A. The ventilation systems shall be balanced in accordance with the latest edition of standards published by the Associated Air Bal- ance Council (AABC), the National Environmental Bal- ancing Bureau (NEBB), or the Testing, Adjusting and Balancing Bureau (TABB). Air balance tolerancing val- ues shall not result in noncompliance of the minimum required pressurization per Table 4-A.

407.4.1 Design of the ventilation system shall provide air movement that is generally from clean to less clean areas.

407.4.1.1 All air distribution devices and supply air outlets shall meet the requirements of ASHRAE 170, Section 6.7.2 and Table 6-2.

407.4.1.2 Supply outlets and return and exhaust air inlets shall be located to prevent short-circuiting.

407.4.1.3 Air supplied to operating rooms, cesarean operating rooms, cardiac catheterization labs, sur- gical cystoscopy rooms, delivery rooms, and class 3 imaging shall be delivered by a primary supply dif- fuser array in accordance with ASHRAE 170, 7.4.1.

407.4.1.4 Air supplied to procedure rooms and Class 2 imaging shall be delivered over the patient table. Return or exhaust inlets shall be located at the perimeter of the room on a minimum of two sides to provide air movement from clean to less clean.

407.4.1.5 At least two exhaust or recirculation air inlets of equal capacity shall be provided on oppo-

78 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

site corners in all operating rooms, cesarean oper- ating rooms, cardiac catheterization labs, surgical cystoscopy rooms, delivery rooms and class 3 imag- ing. All air inlets in the room shall be located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor.

407.4.1.6 Morgues and autopsy rooms shall exhaust air through an autopsy table designed for this pur- pose or through low sidewall exhaust inlets located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor.

407.4.1.7 Room supply air outlets and room recir- culation and exhaust air inlets installed in nonsensi- tive areas shall be located not less than 3 inches (76 mm) above the floor.

Exception: For airborne infection isolation rooms and protective environment rooms, see Sections

407.4.2 Corridors shall not be used to convey supply, return, transfer or exhaust air to or from any room per the California Building Code.

Exceptions:

(1) Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such corridors is permitted where allowed by the Califor- nia Building Code. The corridor air balance shall be equal based on the total net transfer air to or from the corridor.

(2) Air transfer caused by pressure differentials in rooms required to have a positive or negative air balance by Table 4-A.

407.4.3 No space above a ceiling may be utilized as an outside-air, relief-air, supply-air, exhaust-air, or return- air plenum.

Exception: Designs specifically approved by the enforc- ing agency. 407.4.4 Air from a patient room, exam room, treatment room shall not be transferred to another similar room without first having passed through air filters as required by Table 4-B or Table 4-C. 407.4.5 Recirculating Room Units. Recirculating room units shall be permitted to provide a portion of the total air changes for a space in excess of the minimum outside air changes where indicated with a “yes” in the “Recirculated Room Units” column of Table 4-A. The fol- lowing conditions shall be met: (1) not receive nonfiltered, nonconditioned outdoor air; (2) shall serve only a single space; and (3) provide minimum MERV 8 filtration upstream of any surface that is designed to condense water. OSHPD 2 spaces shall be permitted to provide the manufac- turer’s recommended filter for airflow passing over any surface that is designed to condense water. (4) Coils designed not to condense water shall maintain surfaces above the dew point temperature.

407.4.5.1 Recirculating Room Units for Unoc- cupied Spaces. For normally unoccupied spaces not listed in Table 4-A and not directly connected to a patient care area, the minimum filtration for a recir- culating room unit may be as recommended by the equipment manufacturer.

407.5.1 Variable Air Volume Systems (VAV). Variable air volume systems subjecting the patient to a fluctuating air movement are not acceptable for airborne infection isolation rooms, protective environment rooms or those critically sensitive areas listed in Section 322.0. For non- sensitive areas, variable air volume systems meeting the following criteria can be considered:

407.5.1.1 The VAV system shall comply with code requirements for outside air, total air, and pressure relationship through the full range of operation from

minimum to maximum.

407.5.1.2 The central return or exhaust fan shall be controlled to accomplish the variable air volume requirements of the individual rooms served by the fan as described in Section 407.5.1.3.

407.5.1.3 Spaces with pressure requirements per Table 4-A shall utilize an automatic modulating damper in the return or exhaust air for each space. The damper will modulate from full open to minimum position in conjunction with the supply air VAV ter- minal equipment to maintain space pressurization.

407.5.1.4 Sensitive areas or rooms shall be provided with controls on the return or exhaust duct system to maintain constant air flows.

407.5.1.5 Return air controls shall be provided for each system, floor or area with similar conditions.

407.6.1 Systems with economizers shall include modu- lating relief and/or return fans to ensure compliance with the pressure requirements of spaces listed in Table 4-A.

407.7.1 Where indicated with a “yes” in the Unoccupied turndown column of Table 4-A, the number of air changes shall be permitted to be reduced. The following condi- tions shall be met:

(1) The number of air changes may be reduced to 25 per- cent of the indicated value in Table 4-A for pressur- ized spaces when the room is unoccupied.

(2) The number of air changes per hour indicated is reestablished whenever the space is occupied.

(3) The pressure relationship with surrounding rooms is maintained when the air changes per hour are reduced.

(4) All operating, class 3 imaging and cesarean delivery rooms shall maintain a minimum of six air changes per hour of total air when not in use.

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

VENTILATION AIR

ate Care Facilities, and Correctional Treatment Centers.

408.3.1 The air ventilation systems for skilled nursing facilities, intermediate care facilities and correctional treatment centers shall have filter bank efficiencies as listed in Table 4-C.

408.3.2 Airborne infection isolation rooms, protective environment rooms, and sensitive areas in correctional treatment centers shall comply with Section 408.2.

408.4.1 The air ventilation systems for outpatient facil- ities shall have filter bank efficiencies as listed in Table 4-B.

408.5.1 Filters for recirculating room units shall comply with Section 407.4.5. Where Table 4-A does not permit air recirculated by means of room units, room units with filtration per Table 4-B are permitted.

ray or other radiation protection, shall not impair the effec- tiveness of the protection.

of Chapter 6, California Mechanical Code.

airducts shall be designed to withstand the lateral forces as required by the California Building Code, Title 24, Part 2.

[OSHPD 1, 1R, 2, 3, 4 & 5]

tilating systems shall comply with NFPA 99, as required by Section 1224.4.6.4 of the California Building Code.

safety cabinets may be used for normal exhaust of a space pro- vided minimum air change rates are maintained. If air change standards in Table 4-A do not provide sufficient air for proper operation of exhaust hoods and safety cabinets (when in use), supplementary makeup air (filtered and preheated) shall be provided around these units to maintain the required airflow direction and exhaust velocity. Makeup systems for hoods shall be arranged to minimize “short circuiting” of air and to avoid reduction in air velocity at the point of contaminant capture.

shall meet the following standards:

410.3.1 General Standard. Average face velocity shall be at least 75 feet per minute (0.38 meters per sec- ond). Exhaust system shall be separate from the build- ing exhaust system. Exhaust fan shall be located at the discharge end of the system. Exhaust duct system shall be of noncombustible corrosion-resistant material as required to meet the planned usage of the hood.

<

<

<

407.8.1 The outdoor air intake design for air handling systems shall be set to maintain the intake air rate to equal or exceed the building exhaust under all conditions including variable air volume and unoccupied turndown.

manufacturer and shall be based on ASHRAE 52.2 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size when specifically set forth in these standards.

408.1.1 A filter gauge shall be installed across each fil- ter bank serving central air systems. The gauge shall be red lined or a filter alarm light installed to signal when the recommended maximum static pressure drop has been reached.

408.1.2 Central air-handling systems are defined as any unit requiring duct work on the supply or inlet side that serve more than one room.

408.1.3 Filter banks shall be visually inspected for torn media and bypass in filter frames by means of a flashlight or equivalent, both with fans in operation and stopped. Tears in media and bypass in filter frames shall be elim- inated in accordance with the manufacturer’s directions and the requirements of the enforcing agency prior to commencing operation of the system.

408.1.4 Central air-handling systems shall be maintained in a reasonably clean condition during construction and shall be cleaned as necessary prior to replacement of tem- porary filter used during construction to ensure that clean air will be delivered to the occupied spaces.

408.1.5 Filter bank No. 1 shall be located upstream of the air-conditioning equipment. Filter bank No. 2 and additional filter banks shall be located downstream of the supply fan and all cooling and humidification equipment with efficiencies as indicated in Table 4-B or Table 4-C.

Exception: Humidifiers for local room humidity control may be installed in the supply air duct downstream of the final filter bank where designs are specifically approved by the enforcing agency. Humidification shall be in accor- dance with 320.1.1.

408.1.6 Filter bank No. 2 and additional filter bank media shall be rigid or supported (noncollapsing type) and shall operate on the principles of impingement, straining, and diffusion. Filter bank No. 2 shall have sealing interface surfaces.

408.1.7 HEPA filtration shall be provided in the air ter- minal device where required by Table 4-B.

408.2.1 All air-ventilation systems shall comply with code requirements of this section and shall have filter bank efficiencies as listed in Table 4-B.

80 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

410.3.2 Special Standards for Use with Strong Oxidants. Fume hoods and their associated equipment in the air stream intended for use with perchloric acid and other strong oxidants shall be constructed of stainless steel or other material consistent with special exposures. Hoods and equipment shall be provided with a water wash and drain system to permit periodic flushing of duct and hood. When perchloric acid or other strong oxidants are only transferred from one container to another, stan- dard laboratory fume hoods and the associated equip- ment may be used in lieu of stainless steel construction.

410.3.3 Special Standards for Use with Infectious or Radioactive Materials. Each hood shall have a minimum face velocity of 90 to 110 feet per minute (0.45 to 0.56 meters per second) with suitable pressure-inde- pendent air-modulating devices and alarms to alert staff of fan shutdown or loss of airflow. Each hood shall have filters with a 99.97 percent efficiency (based on the DOP test method) in the exhaust stream and be designed and equipped to permit the safe removal, disposal, and replacement of contaminated filters. Filters shall be as close to the hood as practical to minimize duct contam- ination. Fume hoods intended for use with radioactive isotopes shall be constructed of stainless steel or other material suitable for the particular exposure.

food preparation areas only after it has passed through a fil- ter with at least an 80 percent average efficiency based on ASHRAE 52.2 or a minimum efficiency reporting value (MERV) of 13, based on ASHRAE 52.2.

Exception: For skilled nursing facilities, intermediate care facilities and correctional treatment centers, the air from dining area may be used to ventilate food preparation areas only after it has passed through a filter with a 50 percent average effi- ciency based on ASHRAE 52.2 or a minimum efficiency report- ing value (MERV) of 10, based on ASHRAE 52.2.

[OSHPD 1, 2, 3, 4 & 5]

provided with outdoor air so as to maintain combustion rates of equipment and temperatures in the rooms and in adjoining areas as rated in this chapter.

should not exceed a temperature of 85°F (29.4°C), and suit- able insulation may be required.

generated, where objectional odors or dust are present, or where flammable or toxic gases may accumulate, which are used by health facility personnel or patients, shall be pro-

vided with exhaust ventilation to change the air a minimum of ten times per hour.

pital building or skilled nursing facility in which patients are accommodated, or treated, shall be ventilated with exhaust systems which will provide a minimum of ten air changes per hour and prevent odors from entering patient areas.

1, 2, 3, 4 & 5]

system shall be provided for airborne infection isolation rooms. The dedicated system may serve more than one air- borne infection isolation room, adjoining toilet room and anteroom. The exhaust ducts shall be identified by appro- priate labeling with the words "Caution Airborne Infection Isolation Rooms Exhaust" or similar terminology. Such labeling shall be in a manner which is not readily removable and shall appear on the exhaust duct at intervals of not more than 20 feet (6096 mm) and at least once near each room and each story traversed by the exhaust system. Exhaust fans shall comply with Section 407.1.2. The discharge from exhaust fans shall be located above the roof and shall be located a minimum of 25 feet (7620 mm) from areas that may be occupied, doors, operable windows, outdoor air intakes, or other openings into the building. The exhaust fan dis- charge shall be labeled in a manner which readily identifies the precautions which should be observed. To ensure that the airborne contaminates do not reenter the building, one of the following shall be provided:

414.1.1 Exhaust discharge from fan shall extend at least 10 feet (3048 mm) above the roof and discharge verti- cally upward. Self-draining stacks or equivalent shall be used for rain protection. Rain caps which divert the exhaust toward the roof shall be prohibited.

414.1.2 Exhaust shall discharge above roof level and through an accessible HEPA filter. The HEPA filter shall be located upstream of the exhaust fan and have a mini- mum efficiency of 99.97 percent based on the DOP method in accordance with Mil-Std. 282 or a minimum

efficiency reporting value (MERV) of 17, based on ASHRAE 52.2. Filter gage shall be installed across the filter. For maintenance of air balance relationship, see Section 407.3.1. The 25-foot (7620 mm) dimension required by Section 414.1 may be reduced when a 99.97 percent HEPA filter or a minimum efficiency reporting value (MERV) of 17, based on ASHRAE 52.2 is used and the reduced dimension is specifically approved by the enforcing agency.

inlets shall be located to provide airflow patterns that pre- vent stagnation of the air and eliminate short circuiting of the supply to the exhaust, and minimize exposure of health care workers to airborne infectious particles. Supply-air outlets shall be located at or near the ceiling and at the end of the

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

VENTILATION AIR

airborne infection isolation room which is opposite the head of the bed. Exhaust registers shall be located on the wall behind the patient's head, or as close to that wall as practi- cal and shall be located not less than 3 inches (76 mm) nor more than 24 inches (610 mm) above the finished floor.

Exception: For correctional treatment centers, the location and design of the supply outlets an exhaust or return inlets shall not compromise the safety, security and protection of staff, inmates and property.

4 & 5]

return inlets shall be located to provide airflow patterns that prevent stagnation of the air and eliminate short circuiting of the supply to the exhaust or return. Supply air shall be deliv- ered at or near the ceiling and near the patient's bed. All exhaust or return registers shall be located near the entrance to the protective environment room and not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor. Exception: For correctional treatment centers, the location and design of the supply outlets and exhaust or return inlets shall not compromise the safety, security, and protection of staff, inmates and property.

and Protective Environment Rooms. [OSHPD 1, 2, 3, 4 & 5]

trol, volumetric control, or directional flow measurement shall be provided for each isolation room. The alarm system shall consist of a display monitor located on the corridor wall near the door to the room and a visual and audible alarm which

annunciates at the room and at a nurses' station or other suit- able location that will provide responsible surveillance. A time delay shall be provided to allow for routine openings of doors. The alarm shall annunciate when the supply, return, or exhaust fans are interrupted or when the minimum required pressure differential per ASHRAE 170 between the airborne infection isolation room and corridor or between the protec- tive environment room and corridor is not being met during closed door conditions.

designs are specifically approved by the enforcing agency.

alarm system shall not create false alarms or security haz- ards.

shall be tested and operated to demonstrate to the owner or designated representative that the installation and perform- ance of the system conforms to design intent.

tion Rooms and Protective Environment Rooms.

[OSHPD 1, 2, 3, 4 & 5] Prior to acceptance of the rooms, all

mechanical systems shall be tested, balanced, and operated to demonstrate to the owner or designated representative that the installation and performance of the systems conform to design intent. All testing and balancing shall be performed by a qualified independent agency certified by the Associated Air Balance Council (AABC): the National Environmental Bal- ancing Bureau (NEBB); or the Testing, Adjusting and Bal- ancing Bureau (TABB). Air balance testing shall include a pressure test at all doors serving the isolation, protective envi- ronment, and ante rooms to provide the directional pressure relationships in Section 416.1.

Sterilization Areas. [OSHPD 1, 1R, 2, 3, 4 & 5]

shall be provided with minimum air changes per hour per Table 4-A and be maintained at a negative air balance.

418.2.1 All air from the ETO sterilizer equipment room shall be exhausted to the outside by a dedicated system or other approved method.

418.2.2 The exhaust fan for the dedicated system shall be located at the discharge point of the system and identified as ETO Equipment Room Exhaust. 418.2.3 Discharge Point. The discharge point shall be a minimum of 25 feet (7620 mm) away from any outside intake, operable window or personnel passage.

418.3.1 Aeration Units. The aeration units shall be ven- tilated through a nonrecirculating dedicated ventilation exhaust system. 418.3.2 Capture Box. When the drain is not located in the ETO sterilizer equipment room, ventilation is required by a capture box. 418.3.3 Cylinder Change. When not located in the ETO sterilizer equipment room, exhaust during cylinder change is required by installing a hood that is part of a dedicated ventilation exhaust system, positioned no more than 1 foot (305 mm) above or behind the point where the change of cylinders takes place. 418.3.4 Sterilizer Relief Valve. The ventilation of ster- ilizer relief valve is required through a pipe connected to the outlet of the relief valve exhausted directly to the out- doors at a point high enough to be away from passers by, and not near any windows that open, nor near any air- conditioning or ventilation air intakes. 418.3.5 Ventilation of Sterilizer Door Area. The sys- tem shall be designed to capture the ETO when the door is opened following the completion of the sterilization process. A hood or canopy closed on each end should be installed over the sterilization door. A hood or canopy shall be connected to a dedicated exhaust ventilation system.

connection to the supply cylinders are required to minimize leakage during cylinder change.

82 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

shall be installed to alert sterilizer operating personnel if the air flow falls below design cubic feet per minute (L/s).

over the formulation preparation area by group E, nonaspi- rating supply diffusers. Air shall be returned or exhausted by registers located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor in the cleanup area.

the treatment surface by group E, nonaspirating supply dif- fusers. Air shall be returned or exhausted by registers located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor, adjacent to the treatment sur- face.

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

VENTILATION AIR

TABLE 4-A

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

84 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 4-A (continued)

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

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

VENTILATION AIR

TABLE 4-A (continued)

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

86 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 4-A (continued)

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

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

VENTILATION AIR

TABLE 4-A (continued)

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

88 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 4-A (continued)

PRESSURE RELATIONSHIP AND VENTILATION REQUIREMENTS FOR GENERAL ACUTE CARE HOSPITALS,

SKILLED NURSING FACILITIES, INTERMEDIATE CARE FACILITIES, OUTPATIENT FACILITIES, LICENSED CLINICS,

CORRECTIONAL TREATMENT CENTERS, AND ACUTE PSYCHIATRIC HOSPITALS [OSHPD 1, 2, 3, 4 & 5]

Informative Notes: (1) NR = no requirement

Table 4-A is based on ASHRAE Standard 170-2021, “Ventilation of Healthcare Facilities,” Table 7-1, 8-1, 8-2 and 9-1 with amendments, and it is used with expressed written permission from ASHRAE. Copyright notice for ASHRAE Standards ©ASHRAE, www.ashrae.org. 2021 ASHRAE Standard-170.

Notes for Table 4-A: a. Except where indicated by a “No” in this column, recirculating room HVAC units (with heating or cooling coils) are acceptable for providing that portion of the minimum total air changes per hour that is permitted by Section 407.4.5 . Because of the cleaning difficulty and potential for buildup of contamination, recirculating room units shall not be used in areas marked “No.” Recirculating devices with high-efficiency particulate air (HEPA) filters shall be permitted in existing facilities as interim, supplemental environmental controls to meet requirements for the control of airborne infectious agents. The design of either portable or fixed systems should prevent stagnation and short circuiting of airflow. The design of such systems shall also allow for easy access for scheduled preventative maintenance and cleaning. b. Additional air change, ISO class, continuous pressure monitoring and filtering requirements for compounding areas shall comply with California Board of Pharmacy regulations Title 16 §1735 & §1751, and USP <797> & <800>. Air supplied to the compounding buffer room and ante room must be introduced through 99.97% minimum HEPA filters located in the ceiling. At least 15 air changes per hour (ACPH) shall be provided to nonhazardous drug (non-HD) compounding buffer rooms through the ceiling. The HEPA filtered air from the PEC in the non-HD buffer room, when added to the HVAC-supplied HEPA filtered air, shall increase the total HEPA-filtered ACPH to at least 30. If the PEC is used to meet the minimum total ACPH requirements, the PEC must not be turned off except for maintenance. All hazardous drug (HD) compounding areas and PECs shall be externally vented. For both hazardous and non-haz- ardous compounding, minimum air changes shall be met under dynamic operating conditions as defined by USP. Returns and exhaust grilles shall be mounted low on the wall unless a visual smoke study demonstrates dilution of particles and sweeping out of particles from the entire room. One return/exhaust should be placed near the refrigerator compressor. Anteroom shall have a minimum pressure differential of +0.02 inches water column in relation to the adjacent, non-compounding spaces. Non-HD buffer room shall have a pressure differential of +0.02 to +0.05 inches water column in relation to the ante- room. HD buffer room shall have a pressure differential of -0.01 to -0.03 inches water column in relation to the anteroom. c. The term trauma/resuscitation room as used herein is a first-aid room and/or emergency department room used for general initial treatment of accident victims. The OR within the trauma center that is routinely used for emergency surgery is considered to be an OR by this standard. d. For operating rooms, cardiac catheterization labs, angiography rooms, cystoscopy rooms, delivery rooms, cesarean operating rooms, newborn intensive care, and class 3 imaging provide approximately 15% excess supply air to the room or a sufficient quantity of excess supply air to maintain an appropri- ate positive air balance based on the room tightness and number of doors. For all rooms not listed in this footnote or not listed in Section 322.0 requiring either a positive or negative air balance, provide approximately 10% differential cfm between supply and return/exhaust airflow but not less than 25 cfm differential shall be provided regardless of room size. Room function, size, and tightness may be considered when determining the differential airflow required. Where continuous directional control is not required, variations between supply cfm and return or exhaust cfm shall be minimized in accordance with Section 407.4.1.3.

etween supply and return/exhaust airflow but not less than 25 cfm_ differential shall be provided regardless of room size. Room function, size, and tightness may be considered when determining the differential airflow required. Where continuous directional control is not required, variations between supply cfm and return or exhaust cfm shall be minimized in accordance with Section 407.4.1.3.

e. See Section 414.0 and 416.0 for AII ventilation requirements, including pressure relationship requirements, and Section 415.0 and 416.0 for PE ventilation requirements, including pressure relationship requirements.

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

VENTILATION AIR

f. Higher ventilation rates above the total ach listed shall be used when dictated by the laboratory program requirements and the hazard level of the potential contaminants in each laboratory work area. Lower total ach ventilation rates shall be permitted when a hazard assessment, performed as part of an effective laboratory ventilation management plan per AIHA/ASSE Z9.5 3, determines that either (1) acceptable exposure concentrations in the laboratory work area can be achieved with a lower minimum total ach ventilation rate than is listed in Table 4-A or (2) a demand control approach with active sensing of contaminants or appropriate surrogates is used as described in ASHRAE Handbook—HVAC Applications10, Chapter 16, “Laboratories.” g. Examination rooms programmed for use by patients with undiagnosed gastrointestinal symptoms, undiagnosed respiratory symptoms, or undiagnosed skin symptoms. h. A nonrefrigerated body holding room is applicable only to facilities that do not perform autopsies on-site and use the space for short periods while waiting for the body to be transferred. i. Minimum total air changes per hour (ach) shall be that required to provide proper makeup air to kitchen exhaust systems as specified in Section 511.3. Com- mercial cooking areas shall be designed to prevent odors from entering patient spaces. j. Where the “exhaust directly to Outdoors” column is marked yes, all exhaust air shall be discharged directly to the outdoors and not recirculated to other areas. Recirculation room units may be provided where the column is marked yes provided air is not recirculated to other areas. To satisfy exhaust needs, constant replacement air from the outdoors is necessary when the system is in operation. k. The relative humidity (RH) ranges listed are the minimum and/or maximum allowable at any point within the design temperature range required for that space. l. Systems shall be capable of maintaining the rooms within the range during normal operation. Lower or higher temperature shall be permitted when occupants’ comfort and/or medical conditions require those conditions. m. National Institute for Occupational Safety and Health (NIOSH) criteria documents 11 regarding occupational exposure to waste anesthetic gases and vapors and control of occupational exposure to nitrous oxide indicate a need for both local exhaust (scavenging) systems and general ventilation of the areas in which the respective gases are used. ( Informative Note: Refer to NFPA 99 [ 2024 ] for other requirements.) n. If pressure-monitoring device alarms are installed, allowances shall be made to prevent nuisance alarms. Short-term excursions from required pressure relationships shall be allowed while doors are moving or temporarily open. Simple visual methods such as smoke trail, ball-in-tube, or flutterstrip shall be permitted for verification of airflow direction. o. Surgeons or surgical procedures may require room temperatures, ventilation rates, humidity ranges, and/or air distribution methods that exceed the minimum indicated ranges. p. Treatment rooms used for bronchoscopy shall be treated as bronchoscopy rooms. Treatment rooms used for procedures with nitrous oxide shall contain provisions for exhausting anesthetic waste gases. q. In a recirculating ventilation system, HEPA filters shall be permitted instead of exhausting the air from these spaces to the outdoors, provided that the return air passes through the HEPA filters before it is introduced into any other spaces. The entire minimum total air changes per hour of recirculating airflow shall pass through HEPA filters. When these areas are open to larger, nonwaiting spaces, the exhaust air volume shall be calculated based on the seating area of the waiting area. ( Informative Note: The intent here is to not require the volume calculation to include a very large space [e.g., an atrium] just because a waiting area opens onto it.) r. Exhaust rate shall meet or exceed local requirements. s. For intermediate care, labor/delivery/recovery rooms, and labor/delivery/recovery/postpartum rooms, four total ach shall be permitted when supplemental heating and/or cooling systems (radiant heating and cooling, baseboard heating, etc.) are used. t. The protective environment airflow design specifications protect the patient from common environmental airborne infectious microbes (i.e., Aspergillus spores). The anteroom shall have negative air pressure in relation to the protective environment room. A door louver, transfer grille, or other acceptable means may be provided to allow for airflow from the protective environment room to the anteroom. The protective environment room shall have positive pres- sure in relation to the anteroom and adjoining toilet room. Recirculation HEPA filters shall be permitted to increase the equivalent room air exchanges; however, the outdoor air changes are still required. Constant-volume airflow is required for consistent ventilation for the protected environment. The pressure relationship to adjacent areas shall remain unchanged if the protective environment (PE) room is used as a normal patient room. Rooms with reversible airflow provisions for the purpose of switching between PE and AII functions shall not be permitted. u. The AII room described in this standard shall be used for isolating the airborne spread of infectious diseases, such as measles, varicella, or tuberculosis. The airborne infection isolation room shall have negative pressure in relation to the anteroom, and the adjoining toilet room shall have negative pressure in rela- tion to the airborne infection isolation room. Supplemental recirculating devices using HEPA filters shall be permitted to recirculate air within the AII room to increase the equivalent room air exchanges; however, the minimum outdoor air changes of Table 7-1 are still required. When the AII room is not used for airborne infection isolation, the pressure rela

all have negative pressure in rela-_ tion to the airborne infection isolation room. Supplemental recirculating devices using HEPA filters shall be permitted to recirculate air within the AII room to increase the equivalent room air exchanges; however, the minimum outdoor air changes of Table 7-1 are still required. When the AII room is not used for airborne infection isolation, the pressure rela

all have negative pressure in rela-_ tion to the airborne infection isolation room. Supplemental recirculating devices using HEPA filters shall be permitted to recirculate air within the AII room to increase the equivalent room air exchanges; however, the minimum outdoor air changes of Table 7-1 are still required. When the AII room is not used for airborne infection isolation, the pressure relationship to adjacent areas, when measured with the door closed, shall remain unchanged. v. Room temperature ranges that exceed the minimum indicated range shall be permitted if required by the laboratory program or laboratory equipment. w. The requirement that all room air be exhausted directly to outdoors applies only to radiology waiting rooms programmed to hold patients who are waiting for chest x-rays for diagnosis of respiratory disease. x. If the planned space is designated in the organization’s operational plan to be used for both bronchoscopy and gastrointestinal endoscopy, the design parameters for “bronchoscopy, sputum collection, and pentamidine administration” shall be used. y. For single-bed patient rooms using Group D diffusers, a minimum of six total ach shall be provided and calculated based on the volume from finished floor to 6 ft (1.83 m) above the floor. z. See AAMI Standard ST79 [12] for additional information for these spaces. aa. Nurse station pressure relationship and ventilation requirements shall match the area in which it is located. bb. Lower total ach ventilation rates shall be permitted when use of the ASHRAE Standard 62.1 1, Section 6.5, “Exhaust Ventilation,” Performance Compliance Path determines that concentration of the contaminants of concern is lower than the corresponding concentration of interest. In addition to other contaminants of concern required by Standard 62,1 Section 6.5.2, the following contaminants of concern shall be considered for the space and maintained not greater than the concentration level indicated: hydrogen peroxide 1 ppm; glutaraldehyde 0.05 ppm; ethyl alcohol 1000 ppm; isopropyl alcohol 400 ppm. ( Informative Note: Listed concentrations of interest were determined by ACGIH [2001]; see Informative Appendix E.) cc. HD segregated compounding area shall have a differential pressure of -0.01 to -0.03 inches water column in relation to adjacent areas and a minimum of 12 air changes per hour. dd. The requirements for the non-HD segregated compounding area shall meet the minimum requirements for the room which it is located. ee. Informative Note: Parenthetic notations following a space name are references to the relevant California Building Code sections from Chapter 12 . These paragraph references are provided to the user to aid in the application of design requirements. Functions from 1225, 1226, 1227, or 1228 not specifically identi- fied in the table can refer to the appropriate section from 1224. ff. If this space uses unoccupied turndown it shall include time-delay controls such that turndown does not occur for the first 20 minutes after the space becomes unoccupied. ( Informative Note: The 20 minute delay approximates the time required for 90% reduction in airborne contamination at 6 ach, assuming perfect mixing.) gg. Intensive care patient rooms that contain a modular toilet/sink combination unit within the room shall be provided with a minimum of 75 cfm (35.4 Lis) of exhaust directly over the modular toilet/sink combination unit.

comes unoccupied. ( Informative Note: The 20 minute delay approximates the time required for 90% reduction in airborne contamination at 6 ach, assuming perfect mixing.) gg. Intensive care patient rooms that contain a modular toilet/sink combination unit within the room shall be provided with a minimum of 75 cfm (35.4 Lis) of exhaust directly over the modular toilet/sink combination unit.

90 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 4-B

FILTER EFFICIENCIES FOR CENTRAL VENTILATION AND AIR-CONDITIONING SYSTEMS IN GENERAL ACUTE CARE HOSPITALS, OUTPA- TIENT FACILITIES, LICENSED CLINICS AND ACUTE PSYCHIATRIC HOSPITALS [1] [OSHPD 1, 3 & 5]

1 Based on ASHRAE 52.2. 2 A.T.D. – Air terminal device serving the room or space. 3 HEPA filters are those filters that remove at least 99.97% of 0.3 micron sized particles at the rated flow in accordance with the testing methods of IEST RP- CC001. 4 HEPA filters shall be located in the air terminal device of the room served. 5 HEPA filters shall be located in the air terminal device of the room served. HEPA filters shall be permitted to be located in the air handling unit subject to the exception in ASHRAE 170, Section 7.2.2(c). HEPA filter installation shall be designed and equipped to permit safe removal, disposal and replace- ment of filters. 6 The numbers in parentheses represent MERV rating based on ASHRAE 52.2. 7 Additional prefilters with a minimum efficiency of MERV 8 may be used to reduce maintenance for filters.

TABLE 4-C

FILTER EFFICIENCIES FOR CENTRAL VENTILATION AND AIR-CONDITIONING SYSTEMS IN SKILLED

1 Based on ASHRAE 52.2. 2 Filters are not required for evaporative coolers serving laundries. 3 The numbers in parentheses represent MERV rating based on ASHRAE 52.2. 4 Additional prefilters with a minimum efficiency of MERV 8 may be used to reduce maintenance for filters.

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

VENTILATION AIR

TABLE 402.1

MINIMUM VENTILATION RATES IN BREATHING ZONE

[ASHRAE 62.1: TABLE 6-1]

92 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 402.1 (continued)

MINIMUM VENTILATION RATES IN BREATHING ZONE

[ASHRAE 62.1: TABLE 6-1]

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

VENTILATION AIR

TABLE 402.1 (continued)

MINIMUM VENTILATION RATES IN BREATHING ZONE

[ASHRAE 62.1: TABLE 6-1]

For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s Notes: 1 Outpatient facilities to which the rates apply are freestanding birth centers, urgent care centers, neighborhood clinics and physicians offices, Class 1 imaging facilities, outpatient psychiatric facilities, outpatient rehabilitation facilities, and outpatient dental facilities. 2 The requirements of this table provide for acceptable IAQ. The requirements of this table do not address the airborne transmission of airborne viruses, bacteria, and other infectious contagions. 3 These rates are intended only for outpatient dental clinics where the amount of nitrous oxide is limited. They are not intended for dental operatories in institutional buildings where nitrous oxide is piped.

94 2025 CALIFORNIA MECHANICAL CODE

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

VENTILATION AIR

TABLE 403.2.2 ZONE AIR DISTRIBUTION EFFECTIVENESS [ASHRAE 62.1: TABLE 6-4]

For SI units: °C = °F( [5] / 9 ), 1 foot per minute = 0.005 m/s, 1 foot = 304.8 mm

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

VENTILATION AIR

TABLE 403.7

MINIMUM EXHAUST RATES

[ASHRAE 62.1: TABLE 6-2]

For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ]

Notes: 1 Stands where engines are run shall have exhaust systems that directly connect to the engine exhaust and prevent escape of fumes. 2 Where combustion equipment is intended to be used on the playing surface, additional dilution ventilation, source control, or both shall be provided. 3 Exhaust shall not be required where two or more sides compose walls that are at least 50 percent open to the outside. 4 Rate is per water closet, urinal, or both. Provide the higher rate where periods of heavy use are expected to occur. The lower rate shall be permitted to be used otherwise. 5 Rate is for a toilet room intended to be occupied by one person at a time. For continuous system operation during hours of use, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used. 6 See other applicable standards for exhaust rate. 7 For continuous system operation, the lower rates shall be permitted to be used. Otherwise the higher rate shall be used. 8 Exhaust air that has been cleaned to meet Class 1 criteria from Section 403.9 shall be permitted to be recirculated. 9 Rate is per showerhead. 10 [HCD 1 & HCD 2] A bathroom is any room containing a bathtub, a shower, a spa, or a similar source of moisture. 11 [HCD 1 & HCD 2] ANSI/ASHRAE 62.2: Tables 5.1 and 5.2.

96 2025 CALIFORNIA MECHANICAL CODE

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

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE