Can someone please clarify NOx for me...?

[David Meiland]

I'm in the market for a combustion analyzer. There are a number of models in the $500-1500 range, and one of the apparent differences is whether the unit filters nitrogen oxides before the gas reaches the CO sensor, and/or whether the unit displays an NOx reading. From what little I've read the presence of NOx can lead to an erroneous CO reading if there's no filter.... but many of the available tools do not do the filtering, although you can buy an inline filter and add it to your instrument if you want. I'm not an HVAC tech and don't plan to become one, but as part of energy audits I need accurate CO readings in ambient air and in the flue, as well as combustion efficiency. I don't want to buy an $1100 tool if a $500 tool will do. Can someone break this down for me?

[Terence McCann]

http://www.aikencolon.com/combustion-analyzers.html