COSTARŽ Carbon Monoxide Ventilation Control 24VC-e by Quantum Group, unlike many competitors products, is calibration free;i,e, no gas test. Just replacing the sensor every 3 years saves a lot of maintenance cost. Each individual sensor is factory calibrated. Neither expensive field adjustments nor calibration kits are required. A signal indicating sensor replacement is given when necessary. There is a 12 Year PC board end-of-life. The unit will give a warning 60 days prior to the PCB end-of-life.