We have 50+ buildings and are looking at standardizing our brand and type of CO2 sensor. We currently have multiple brands/types (many of which need replacement or calibration). Moving forward, we would like to stick to one brand/type as this would make the replacement and/or calibration process a lot easier. In your opinion, what are the best CO2 sensors in regards to value (cost vs. performance), lifespan, warranty, ease of calibration, length of time between calibration etc. I would also like to know what the general life expectancy of a CO2 sensors are? Which brands provide longer life expectancies? How long before most CO2 sensors need to be calibrated? Which brands seem to need less calibration over time? 90% of our CO2 sensors are duct mount. The signal can be either 4 to 20 mA or 0 to 10 VDC and an accuracy of +/- 100 PPM will do.