This would be overkill but if you don't mind spending alot of money, try a
LICOR.  Otherwise I would think any NDIR type would be fine.  A sensor with
some long term drift is not a big problem if you have some calibration
gases, but then that would be overkill too.

Mark


 >Can anyone suggest a good CO2 sensor, accuracy at 1000ppm must be better
 >than 10% after 1 year. Intended use is in a greenhouse to control the
 >inflow of heater exhaust gasses.
 >I don't expect anything cheap.

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