How often?
Short answer: the system must be inspected and tested at least annually, and each sensor must be calibrated at the frequency the manufacturer specifies, which is typically every 6 to 12 months. Most enclosed garages land on an annual service, and some sensor models require more.
Where the requirement comes from
California Fire Code §916.11 sets two separate obligations. Inspection and testing of the gas detection system: not less than annually. Sensor calibration: at the frequency specified by the sensor manufacturer, with calibration confirmed at installation. The code deliberately defers to the manufacturer on calibration interval, which is why there is no single number that applies to every building. Your interval depends on the sensor you own.
| Item | Typical interval | Set by |
|---|---|---|
| System inspection and test | Annually, minimum | Fire code |
| Sensor calibration | Every 6 to 12 months | Sensor manufacturer |
| Sensor replacement | Every 2 to 7 years | Sensor manufacturer |
Why sensors drift, even when nothing looks wrong
Garage CO sensors are electrochemical. They contain a chemical cell that reacts to carbon monoxide and produces a small current, and that cell degrades with time, temperature, humidity and exposure. The degradation is invisible. The panel keeps showing a reading. The reading is simply no longer correct, and it drifts in whichever direction the cell has aged, so a sensor can read low and fail to trigger the fans, or read high and run the fans constantly for no reason.
This is the part that surprises property managers most often: there is no warning light for a sensor that is quietly wrong. The only way to know is to apply certified span gas and see what the sensor reports.
What happens when calibration is skipped
- Compliance: you cannot demonstrate an annual test, which is what an inspector asks for
- Safety: a drifted sensor may not call for ventilation when CO is actually building
- Cost: a sensor reading high runs your exhaust fans far more than needed, on your power bill
- Liability: if someone is harmed, the maintenance record is the first document requested
How to find out where your building stands
Look for a service report with a date and a list of sensors on it. If the last one is more than a year old, or nobody can find one, the system is due.
Most parking garages go more than a year between calibrations. Fire code requires testing at least annually, so the typical garage is already past due.
ACES Monitoring calibrates with certified test gas, verifies that each sensor actually drives the ventilation response at setpoint, and issues an audit-ready report. Calibration typically runs $150 to $200 per sensor depending on system and sensor count. Most garages run 10 to 20 sensors, and we service sites with more than 100.
Sources: California Fire Code §916.11 · sensor manufacturer service literature.
Common questions
How often must CO sensors be calibrated?
California Fire Code 916.11 requires the gas detection system to be inspected and tested at least annually, and each sensor to be calibrated at the frequency specified by its manufacturer, typically every 6 to 12 months.
Do CO sensors expire?
Yes. Garage CO sensors are electrochemical and the sensing cell degrades over time. Manufacturers generally specify replacement every 2 to 7 years depending on the model and environment.
Can maintenance staff calibrate CO sensors?
Not meaningfully. Calibration requires certified span gas with a current fill date, the correct regulators and delivery equipment for each sensor type, and knowledge of the panel programming. A visual or functional check is not a calibration.
What does CO sensor calibration cost?
Calibration typically runs $150 to $200 per sensor depending on the system, the sensor type and the number of sensors. Most garages run 10 to 20 sensors.
Talk to a gas monitoring specialist
Tell us the building and how many sensors you have. We will tell you what service it needs and what it costs, no pressure.