Oxygen (O2) versus Carbon Dioxide (CO2) Measurements in Combustion Analysis

Oxygen vs Carbon Dioxide Measurements in Combustion Analysis

In Tech / Application Notes by Bacharach

The most accurate and efficient method for performing a combustion analysis is to measure oxygen (O2) directly. Bacharach combustion analyzers use electrochemical O2 sensors to perform this measurement, whereas other analyzers may only measure carbon dioxide (CO2).

By measuring O2, HVAC technicians will optimize their time, decrease fuel costs for their customers and mitigate potential safety risks.

Changes in O2 concentrations are much larger and easier to read than the comparative changes in CO2 for a given excess air level. O2 readings are also less sensitive to variations in the chemical composition of the fuel. When combustion is perfect or when the process is burning excess fuel, the O2 measurement will decrease to zero percent. When combustion is running on the preferred excess air side of the process, the O2 reading will increase. These reliable patterns make monitoring a combustion process simple and easy (see “B” in the figure below).

On the other hand, CO2 readings can be the same on both the excess fuel and excess air sides of the combustion process (see “A” in the figure below). It is only possible to determine what the CO2 measurement is telling you by making extra adjustments to the appliance and the analyzer – costing the technician more time and money.

Chart illustrating the concentration of gases during the combustion process.

Performing adjustments based on the wrong CO2 readings wastes fuel, produces more carbon monoxide (CO), wastes the technician’s time and increases risks of CO poisoning. While oxygen sensors may have a shorter lifespan than their CO2 counterparts, the improved accuracy and time savings make it well worth the trade-off.

Bacharach also makes it easy for HVAC technicians to replace their analyzer’s O2 sensors in the field to prevent downtime.