The 2025 California Building Standards Code (Title 24) updates include important clarifications and enforcement emphasis for carbon monoxide (CO) alarms and detection systems.
This article breaks down:
- When CO alarms/detection are required under 2025 CBC Section 915 and 2025 CFC Section 915
- How the IFC Section 915 model requirements (the backbone of many state fire codes) broaden the “when required” scope beyond just dwelling units
- Power and interconnection rules
- Enclosed parking garage CO sensor requirements and how California coordinates to CMC 403.7.2
- How NFPA 72 (2022) applies for inspection, testing, and maintenance where applicable
When Are Carbon Monoxide Alarms / Detection Required? (Two-Lane Approach)
CO requirements get mis-described a lot because designers mix “dwelling unit alarm rules” with “broader building CO detection rules.” To keep your plans plan-check-proof, think in two lanes:
Lane 1: Dwelling Units & Sleeping Units (CBC 915 focus)
Under 2025 CBC Section 915, CO alarms are commonly required in dwelling units/sleeping units when CO exposure risk sources are present, such as fuel-burning appliances and attached garages communicating with the dwelling unit. (CBC 915 framework.)
Common residential triggers include:
- Fuel-fired appliances
- Gas fireplaces
- Fuel-burning forced-air furnaces
- Attached garages that communicate with the dwelling unit
 |
| Listed combination smoke and carbon monoxide alarms are permitted when installed in accordance with CBC 915 and CFC 915 requirements. |
Lane 2: Broader “Interior Space” Requirements (CFC 915 / IFC 915 scope)
Important: The IFC Section 915 (model code basis for many state fire codes, including California’s structure) is broader than only dwelling-unit triggers. It addresses CO detection requirements for new and existing buildings where interior spaces are exposed to CO sources (direct sources, adjacent spaces with communicating openings, and forced-air-related source conditions). In other words: your project may require CO detection even when it doesn’t look like a classic “residential attached garage” situation.
Required Locations (CBC 915.2 concept + CFC/IFC placement logic)
Dwelling units (CBC approach): When required, CO alarms are typically installed:
- Outside each separate sleeping area in the immediate vicinity of bedrooms
- On every occupiable level of the dwelling unit, including basements
- Additional devices may be required where fuel-burning appliances are located within bedrooms or attached bathrooms (project/AHJ dependent)
Broader interior spaces (CFC/IFC approach): Where CO detection applies to interior spaces exposed to CO sources, design should address:
- Spaces containing CO-producing equipment (direct source locations)
- Adjacent spaces with communicating openings where CO could migrate
- Forced-air pathways that can distribute CO to other areas
Always coordinate exact device placement with manufacturer instructions, the adopted code language, and AHJ expectations.
Power & Interconnection (CFC 915.4 + CBC 915 structure)
Power Source (CFC 915.4.1)
CO alarms shall receive primary power from building wiring where such wiring is served from a commercial source, with battery backup where required.
Interconnection (CFC 915.4.4 / CBC 915 framework)
Where more than one CO alarm is required, alarms must be interconnected so activation of one activates all required alarms within the applicable unit/area. California’s 2025 cycle specifically retains clarifying language around interconnection implementation.
Combination Smoke/CO Devices
Combination smoke/CO alarms are permitted where properly listed/approved and installed per manufacturer instructions and adopted code requirements.
Enclosed Parking Garages – CO Sensors and Ventilation Control (CFC 915.6.1 + CMC 403.7.2)
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| Carbon monoxide sensors installed in enclosed parking garages to control ventilation systems in coordination with CFC 915.6.1 and CMC 403.7.2. |
This is where a lot of projects get tripped up.
- Model code note: The IFC framework ties enclosed garage gas detection to mechanical ventilation code references (model mechanical code structure).
- California note: In the 2025 cycle, California explicitly coordinates enclosed garage detector maintenance expectations through CFC 915.6.1 with reference to CMC 403.7.2.
Key takeaway: Treat enclosed garage CO sensors primarily as a mechanical ventilation control / IAQ scope unless the AHJ/EOR requires FACU integration. If integrated into the fire alarm system, document supervision, pathway, and point type clearly.
NFPA 72 (2022) – How to Reference It Without Getting Burned
Older references commonly point to NFPA 720 for CO detection. NFPA has stated that NFPA 720 requirements were incorporated into NFPA 72.
Safe spec language:
- Install per the adopted California codes (CBC/CFC) and manufacturer instructions.
- Where CO detection/notification equipment is part of a signaling system, perform inspection/testing/maintenance per NFPA 72 (2022) as applicable.
2022 vs 2025 Code Comparison (CBC/CFC CO Requirements)
| Topic | 2022 Cycle (General) | 2025 Cycle (What to watch) | Plan-Check Proof Note |
|---|---|---|---|
| Scope / “When Required” | Commonly described as dwelling-unit driven in many field guides. | Must describe both: dwelling/sleeping units (CBC) AND broader interior-space CO exposure conditions (CFC/IFC framework). | Write the “two-lane” note on the cover sheet. |
| Power | Hardwired where served by commercial power; battery backup where required. | Same concept; cite CFC 915.4.1 explicitly for reviewer confidence. | Call out power method and any remodel constraints. |
| Interconnection | Interconnect multiple required alarms. | California emphasizes implementation clarity; cite CFC 915.4.4 for consistency. | State “hardwired or listed wireless” and show it on plans. |
| Enclosed Parking Garages | Often treated as mechanical/energy controls work, coordinated across disciplines. | CFC 915.6.1 coordinates maintenance expectations to CMC 403.7.2 in California. | Add a garage SOO and fail-safe behavior. |
| NFPA Reference | NFPA 720 often cited historically. | NFPA states CO requirements are incorporated into NFPA 72; cite NFPA generally unless quoting licensed text. | Write “NFPA 72 (2022) where applicable + manufacturer instructions.” |
Plan Review Notes (Copy Into Drawings)
CARBON MONOXIDE (CO) – 2025 CBC / 2025 CFC GENERAL NOTES 1. Provide CO alarms and/or CO detection where required by the adopted codes: • 2025 CBC Section 915 for dwelling units and sleeping units (life-safety CO alarms). • 2025 CFC Section 915 for interior spaces exposed to CO sources (CO detection scope). Reference IFC Section 915 as the model basis for broader CFC 915 scope where applicable. 2. Power: CO alarms shall receive primary power from building wiring where served by a commercial source, with required secondary power/battery backup. (CFC 915.4.1) 3. Interconnection: Where multiple CO alarms are required, alarms shall be interconnected so that activation of one activates all required alarms within the applicable unit/area. (CFC 915.4.4 / CBC 915 framework) 4. Combination Smoke/CO Alarms: Combination devices shall be listed/approved and installed in accordance with adopted code requirements and manufacturer instructions. 5. Enclosed parking garages (where applicable): CO/NO2 detectors used for ventilation control shall be coordinated with mechanical design. In California, detector maintenance expectations coordinate through CFC 915.6.1 with CMC 403.7.2. 6. Inspection, testing, and maintenance: Perform per adopted code requirements, manufacturer instructions, and NFPA 72 (2022) where applicable. Note: NFPA states NFPA 720 requirements were incorporated into NFPA 72.
Garage CO Sensor Sequence of Operations (Typical)
ENCLOSED PARKING GARAGE – CO SENSOR CONTROL (TYPICAL) GENERAL - Provide CO (and where applicable NO2) sensors for ventilation control. - Coordinate with mechanical ventilation controls per CMC 403.7.2. - Maintain per CFC 915.6.1 and manufacturer requirements. CONTROL LEVELS (VERIFY WITH EOR / MECH DESIGN) Low CO Setpoint (typical 25–35 ppm; adjustable): - Enable exhaust fans at LOW SPEED (Stage 1). - Enable supply/make-up air as required. - Send RUN status to BAS if provided. High CO Setpoint (typical 50–100 ppm; adjustable): - Enable exhaust fans at HIGH SPEED (Stage 2). - Flag high-level condition to BAS (supervisory/trend). - Continue ventilation until levels fall below reset threshold. RESET / PURGE DELAY - After CO drops below LOW setpoint, continue fans for timed purge (typical 5–15 minutes) then return to standby. FAIL-SAFE - On sensor fault, power loss, or communications loss, command minimum fan operation (Stage 1) and report TROUBLE/FAULT to BAS. MAINTENANCE - Test/calibrate per manufacturer interval. - Maintain per adopted code requirements and NFPA 72 (2022) where applicable.
Keywords: 2025 California carbon monoxide requirements, CBC 915 carbon monoxide alarms, CFC 915 carbon monoxide detection, IFC 915 carbon monoxide code, CMC 403.7.2 garage ventilation control, NFPA 72 (2022) carbon monoxide.
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