“We check the CO sensors” can mean two very different things. One of them satisfies the fire code and tells you the system works. The other is a person looking at a panel. Here is the difference.

What a proper calibration involves

• Certified span gas applied to each sensor. A known concentration of CO is delivered to the sensor and the reading is compared to it. This is the only way to learn what the sensor actually reports, because an electrochemical cell drifts silently.
• Adjustment to spec, or replacement. If the sensor can be brought back into tolerance, it is calibrated. If the cell is spent, it is replaced. Manufacturers generally specify replacement every 2 to 7 years.
• Verified ventilation response. The point of the system is that fans start when CO reaches setpoint. That has to be proven at the fan, not assumed at the panel.
• Control logic and fault checks. Sensors sit in wired loops with thresholds and fail-safe behavior. Setpoints, alarm levels and trouble conditions get verified.
• A dated report, per sensor. Every sensor listed, what it read, what was done, what failed. This is your compliance record and your defense.

What does not count

A visual inspection. A panel with no alarms showing. A “functional check” that confirms a sensor is powered and communicating but never introduces gas. Pressing test on the panel. None of these tell you whether the sensor reports 35 ppm when 35 ppm is present, which is the only question that matters.

Why in-house staff cannot do this

Not a knock on maintenance teams. It requires certified calibration gas with a current fill date, regulators and delivery equipment for each sensor type, knowledge of the specific panel’s programming, and documentation that will hold up with an inspector. It is specialized equipment for one task performed once a year, which is why it does not make sense to own.

Why a gas monitoring specialist and not a general mechanical contractor

Mechanical contractors often add CO service onto an HVAC contract. In practice many arrive without calibration gas and verify only that the equipment runs, which is a mechanical check, not a gas calibration. ACES Monitoring does gas monitoring exclusively, has done it for over 30 years, and carries the gas and the equipment on every truck.

What you receive

• Full sensor inspection and calibration with certified test gas
• A confirmation report documenting every sensor and any issue found
• Audit-ready records for inspectors and the fire department