E Instruments BTU700-3 Combustion Analyzer is an all in one economical residential combustion analyzer that does set-ups, servicing, and maintenance of boilers and burners. The E Instruments BTU700-3 measures O2, CO2, CO, Combustion Efficiency & Upgradeable to NO/NOx, Efficiency, Excess Air, Tair Tgas, DRAFT, Differential Pressure, and Ambient CO to handle any test that might come up in the field. The E Instruments BTU700-2 Combustion Analyzer includes unbreakable metal probe connections, field replaceable pre-calibrated sensors, and a magnetic rubber boot for hands free use.