What occupancy types trigger DCV requirements under California Title 24?

Title 24 Section 120.1(d) requires demand-controlled ventilation for zones meeting both conditions: (1) design occupancy density at or above 25 people per 1,000 sq ft, and (2) the zone is served by an HVAC system with an OA economizer or has OA flow that can be modulated by the controls system. Occupancy types commonly triggering DCV include: office conference rooms (120+ sq ft), classrooms and lecture halls, restaurant dining areas (new trigger in 2025 edition), fitness rooms, retail sales floors, and multi-purpose assembly spaces.

Where should CO₂ sensors be placed for Title 24 DCV compliance?

For Title 24 DCV compliance, CO₂ sensors must be placed in the breathing zone - between 3 and 6 feet above the floor and away from supply air diffusers, return air inlets, and operable windows or doors. ASHRAE 62.1 and the California DCV compliance guidance recommend one sensor per zone (per thermostat zone or per DCV control zone). The sensor must be connected to the HVAC controls system and configured to modulate the OA damper or AHU OA volume in response to CO₂ concentration. Sensor setpoints must be set to maintain CO₂ below 1,100 ppm (approximately 700 ppm above outdoor background) or per the project ventilation rate procedure.

What zones are exempt from DCV in California?

Title 24 Section 120.1 and California Mechanical Code exempt the following zone types from DCV requirements: commercial kitchens (grease-laden air systems where OA modulation is not appropriate); laboratories and cleanrooms (minimum OA is driven by fume dilution and contamination control, not occupancy); operating rooms and critical care areas in healthcare facilities (HCAI requires constant minimum OA for infection control); retail areas where occupancy is continuous and highly variable with no defined schedule; and zones already at minimum OA (where the AHU cannot further reduce OA below current levels). Additionally, spaces with exhaust-driven ventilation (e.g., restrooms) are not subject to DCV.

How does DCV interact with HCAI requirements for California healthcare buildings?

California HCAI (Health Care Access and Information, formerly OSHPD) enforces ASHRAE 170 ventilation requirements for licensed healthcare facilities. ASHRAE 170 sets minimum ACH and OA requirements by room type that are higher than standard commercial minimums and must be maintained continuously - they cannot be reduced based on occupancy. As a result, patient care areas, operating rooms, procedure rooms, and isolation rooms are DCV-prohibited zones. Administrative areas, waiting rooms, and break rooms within a healthcare facility that are not patient care spaces may be subject to DCV if they meet the Title 24 occupancy-density trigger.

What energy savings can California building owners expect from DCV?

Energy savings from DCV depend heavily on occupancy patterns. Buildings with variable occupancy - conference rooms, schools, theaters, restaurants - see the highest DCV savings, because they are designed for peak occupancy but are frequently well below peak. CEC studies indicate that DCV can reduce HVAC energy consumption by 10–25% in high-density variable-occupancy zones by reducing the OA that must be conditioned during low-occupancy periods. In offices where occupancy has become highly variable (post-hybrid-work), DCV savings have increased significantly relative to historical baselines.

Energy Code · Ventilation · Published 2026-06-03

Demand controlled ventilation (DCV) for California commercial buildings: Title 24 compliance guide for mechanical contractors

Demand controlled ventilation is one of the most frequently misapplied requirements in California commercial HVAC - both under-specified (missing DCV where it's required) and over-specified (adding DCV to zones where it's prohibited). This guide covers the Title 24 Section 120.1 trigger thresholds, CO₂ sensor placement requirements, the specific zones where DCV must not be used, healthcare facility exceptions under HCAI, and how to document DCV compliance for plan check.

Commercial HVAC ductwork system with demand controlled ventilation CO2 sensor integration — Commercial HVAC duct systems serving high-occupancy zones require DCV under Title 24 Section 120.1 - CO₂ sensors modulate OA damper position to match actual occupancy.

The logic behind DCV: why California requires it

ASHRAE 62.1 - the national ventilation standard California's mechanical code references - requires minimum outside air (OA) ventilation rates based on both the floor area of a zone and the number of occupants. In a conference room designed for 20 people, the minimum OA rate is calculated based on full occupancy - even when the room has only 2 people in it.

Without DCV, that conference room brings in the full design OA whenever the HVAC system is running, regardless of actual occupancy. In California's climate, every cubic foot of OA must be cooled or heated to supply-air temperature - and in summer, that means running more refrigeration to condition OA that isn't needed for the 2 people actually in the space.

DCV solves this by using CO₂ sensors as an indirect measure of occupancy. As CO₂ rises toward 1,100 ppm (approximately 700 ppm above outdoor background, which ASHRAE 62.1 uses as the indicator of inadequate ventilation), the OA damper opens. As CO₂ drops, the OA damper modulates down to minimum. The result is ventilation that tracks actual occupancy rather than design maximum.

The energy savings from DCV are concentrated in zones with highly variable occupancy - conference rooms, classrooms, restaurant dining areas, and fitness spaces. The 2025 Title 24 update expanded DCV requirements to include restaurant dining - a significant change for restaurant TI projects. For a broader overview of the 2025 code updates, see our Title 24 2025 mechanical guide.

Section 120.1(d) DCV triggers: the occupant density threshold

Title 24 Part 6 Section 120.1(d) requires DCV when two conditions are both met:

The zone's design occupant density is at or above 25 people per 1,000 sq ft. This is the key threshold. A zone designed for 25 occupants per 1,000 sq ft means: a 1,000 sq ft zone with 25 or more occupants; a 2,000 sq ft zone with 50 or more occupants; a 500 sq ft conference room with 13 or more occupants. Occupant density is determined by occupancy type from CMC Table 4-4 or by the building designer's stated design occupancy, whichever is greater.
The zone is served by an HVAC system whose OA volume can be modulated. A zone served by a simple constant-volume split system with a fixed OA damper may not be technically capable of DCV without a controls upgrade. Most modern RTUs and AHUs can accommodate DCV with a modulating OA damper and controls interface.

Common zone types that routinely meet the 25/1,000 threshold:

Office conference rooms of any size (CMC Table 4-4 conference occupancy: 50 persons/1,000 sq ft)
Classrooms and lecture halls (35–40 persons/1,000 sq ft)
Restaurant dining areas (70 persons/1,000 sq ft - new to 2025 DCV trigger)
Fitness rooms and exercise studios (25–40 persons/1,000 sq ft)
Retail sales floors in high-density merchandising layouts (40 persons/1,000 sq ft)
Theater lobby and assembly spaces (150 persons/1,000 sq ft)

Office open-plan work areas with standard office furniture (5 persons/1,000 sq ft) typically do not trigger DCV. Individual private offices and small meeting rooms under 120 sq ft often do not trigger DCV at standard occupant counts.

CO₂ sensor placement and setpoint requirements

ASHRAE 62.1 and California's DCV compliance guidance specify where sensors must be placed and how they must be configured to be valid for Title 24 compliance:

Placement

Height: Between 3 and 6 feet above the finished floor - the breathing zone as defined by ASHRAE 62.1.
Location within zone: At least 3 feet from any supply air diffuser or return air grille. Not on an exterior wall with operable windows or exterior doors (thermal stratification and infiltration affect readings).
One sensor per DCV zone. A "DCV zone" is the zone or set of zones controlled by a single OA damper or AHU OA section. In a multi-zone VAV system, each zone served by its own return/OA strategy needs its own sensor if the OA is modulated independently.
For large open spaces (over 1,500 sq ft with variable occupancy distribution), multiple sensors are recommended to avoid a corner sensor failing to detect high occupancy at the center of the space. Title 24 does not mandate multiple sensors per zone, but HERS raters may flag a single sensor in an oddly shaped large space.

Setpoints and calibration

The standard CO₂ control setpoint is 1,100 ppm - approximately 700 ppm above the typical outdoor CO₂ concentration of 420 ppm (2026 outdoor background). At 1,100 ppm, the space is at or near the ASHRAE 62.1 per-person ventilation rate for the stated occupancy.
Sensors must be factory-calibrated and must remain within ±75 ppm of actual CO₂ concentration to satisfy HERS calibration verification. Most NDIR (non-dispersive infrared) CO₂ sensors (Setra, Vaisala, Belimo, ProductLine Solutions) are stable within this tolerance for 3–5 years before recalibration.
HERS raters verify sensor calibration at commissioning by cross-checking against a calibrated reference meter. A sensor more than ±75 ppm off fails the HERS verification.

Zones where DCV is prohibited

The zones where DCV must not be applied are as important as the zones where it must be used. Specifying DCV in a prohibited zone creates a code violation and a commissioning failure:

Commercial kitchens with Type I hoods: The grease exhaust system establishes a dominant airflow pattern in the kitchen, and OA is balanced against the hood exhaust, not against occupancy. DCV on kitchen ventilation would interfere with make-up air balance and potentially cause makeup air unit starvation. CMC Section 511 governs kitchen ventilation separately from Title 24 DCV.
Laboratories with chemical fume hoods: Minimum OA in labs is driven by fume dilution requirements - typically 6–10 ACH minimum. DCV cannot reduce OA below the fume-dilution minimum regardless of CO₂ levels.
Cleanrooms: Cleanroom positive pressure and ISO classification require constant minimum OA and exhaust relationships that cannot be varied by occupancy sensing.
Patient care areas in licensed healthcare facilities: See HCAI section below.
Spaces where 100% OA is required continuously: Welding bays, spray booths, areas with hazardous material storage - any space where the ventilation rate is set by industrial hygiene requirements, not occupancy.

DCV in healthcare facilities: HCAI requirements override Title 24

California HCAI (Health Care Access and Information) regulates the design and construction of licensed healthcare facilities - hospitals, skilled nursing facilities, surgery centers, and other licensed healthcare occupancies. HCAI enforces ASHRAE Standard 170 (Ventilation of Health Care Facilities), which sets minimum ACH and OA requirements by room type.

For patient care spaces under HCAI jurisdiction, ASHRAE 170 minimum OA requirements represent a continuous minimum - they cannot be reduced below the standard values regardless of occupancy. This makes patient rooms, exam rooms, procedure rooms, operating rooms, and isolation rooms DCV-prohibited zones. The minimum OA is always at the ASHRAE 170 value; the CO₂ level is not a relevant variable for the ventilation control strategy in these spaces.

Non-patient-care spaces within a licensed healthcare facility - administrative offices, break rooms, conference rooms, and waiting areas - are not subject to ASHRAE 170 patient-care minimum ACH. These spaces may trigger DCV under Title 24 Section 120.1 if their occupant density meets the threshold. The mechanical contractor must distinguish between licensed patient care space (ASHRAE 170 + HCAI governs, DCV prohibited) and support space (Title 24 governs, DCV potentially required).

For the full HCAI regulatory picture on healthcare HVAC, see our companion article on negative pressure rooms and HCAI requirements.

BAS integration for plan check documentation

Title 24 plan check reviewers and HERS raters both want to see DCV documented in the permit set before construction, not just as a startup-phase item. The following documentation in the mechanical drawings satisfies most California AHJ plan check requirements:

DCV zone identification on the floor plan (or on the mechanical plan) - which zones are DCV-controlled, with occupant density calculation for each
CO₂ sensor locations shown on the plan with mounting height noted
Controls note specifying the CO₂ setpoint (1,100 ppm is standard) and the control action (modulate OA damper from minimum to maximum CFM)
NRCC-MCH-05 (HVAC Controls) form documenting DCV compliance
Reference to NRCA-MCH acceptance test for DCV sensor calibration verification

BAS integration documentation - including the BAS point list confirming CO₂ sensors are connected, and the control logic diagram showing OA modulation - is typically submitted with the controls submittal, not at plan check. However, some AHJs (San Francisco DBI, Oakland) now request the controls sequence of operations at plan check, not just at submittal. Check with the specific AHJ at pre-application if this is a concern. For plan check correction guidance if DCV documentation is flagged, see our mechanical plan check correction letter guide.

Working with Sierra Mechanical on DCV compliance

Our project managers identify DCV-triggering zones at the design-assist stage and coordinate CO₂ sensor specification with the controls contractor before the permit set is submitted. We generate NRCC-MCH-05 documentation as part of our standard Title 24 compliance package. For active projects with DCV scope, request a bid with your floor plan and occupancy schedule. Bid desk: (916) 638-8605.

References: California Energy Code Title 24 Part 6 (2025) § 120.1; California Mechanical Code (2025) Table 4-4; ASHRAE Standard 62.1-2022; ASHRAE Standard 170-2021. Information current as of 2026-06-03.

This article is general guidance. Consult your local AHJ and a licensed mechanical engineer for project-specific DCV requirements.