Hey guys - I've been looking to find an oxygen sensor that fits certain criteria. I've been looking through oxygen sensors on Google and I can't really figure out what kinds of inexpensive oxygen sensors are available that aren't meant to go inside car exhausts. I would really appreciate it if someone here could help me in this regard, or at least post a link to a website that sells sensors which might peddle the kind of sensor I'm looking for! I'm looking to buy just a few now, but in the future, if all goes well, I might be ordering a few thousand. Criteria: Reasonable price (less than $150, excluding shipping, except if shipping costs more than $25) Resistant to and unaffected by soot; sensor will be placed in a house hold chimney and should be well suited to EPA standards of soot in chimney smoke. Sensor's readings should be accurate to within half a percent oxygen concentration in air, or more accurate Sensor's operating temperature must be between 50 C and 500 C (i.e, a sensor that operates at 200 C to 300 C is just fine - we can adjust where we place the sensor in the chimney to allow for temperature adjustment near sensor position) Oxygen sensor will have to deal with the moisture present in a house hold chimney ( Accuracy isn't as important as being rugged and resistant to extreme soot build up. I'm also looking for a carbon monoxide sensor - this would operate in the same conditions as above, but accuracy obviously needs to be much more accurate - measuring on a ppm scale seems to be a good idea for our application. Thanks so much!