Combustion analyzers generate several measurements and calculated values during a test. Understanding how those values relate to one another is essential when evaluating a furnace, boiler or burner.
Rather than focusing on one number, technicians typically need to consider the overall combustion picture.
Here are some of the key parameters you’ll encounter.
Oxygen (O₂)
A combustion analyzer measures the amount of oxygen remaining in the flue gas after combustion.
Why does that matter?
Combustion requires oxygen, but introducing more air than necessary also means additional air must be heated and exhausted through the flue. Too little combustion air, on the other hand, can contribute to incomplete combustion.
O₂ is therefore an important measurement for understanding the relationship between combustion air and fuel.
Carbon Monoxide (CO)
Carbon monoxide is produced by incomplete combustion.
Elevated CO readings can indicate that combustion is not occurring as intended and should be investigated rather than treated simply as an efficiency number.
Potential causes can include issues involving fuel-air mixture, burner condition, draft, venting or other equipment-specific factors.
Because CO presents a serious safety concern, combustion testing and equipment adjustments should be performed by qualified personnel following applicable manufacturer procedures and safety requirements.
Carbon Dioxide (CO₂)
CO₂ is another important component of combustion gases.
On many portable combustion analyzers, CO₂ may be calculated using measured oxygen and information about the selected fuel rather than measured directly.
CO₂ can provide additional insight into combustion conditions, but—as with other combustion parameters—it should be interpreted in context rather than used alone to determine whether a system is operating correctly.
Excess Air
The theoretical combustion process would provide exactly enough air to completely burn the fuel.
Real combustion equipment generally operates with some excess air to help achieve complete combustion.
The challenge is balance.
Insufficient air can contribute to incomplete combustion. Excessive air, however, can reduce efficiency because unnecessary air is heated and sent out through the exhaust.
Natural Resources Canada describes excess air as a commonly used indicator of burner performance in its boiler stack-loss methodology.
Combustion analyzers make this relationship easier to evaluate by using measurements such as O₂ to calculate excess air.
Flue-Gas Temperature
Temperature is another critical part of combustion analysis.
Hot combustion gases leaving through the stack carry energy with them. Natural Resources Canada identifies stack losses as one of the major categories of boiler energy loss and notes that these losses depend on factors including firing conditions and flue-gas temperature.
That doesn’t mean lower stack temperature is automatically better in every situation. Equipment design, operating conditions, condensation, draft and manufacturer specifications all matter.
Instead, temperature should be evaluated alongside the other combustion measurements.
Combustion Efficiency
Many analyzers provide a calculated combustion-efficiency value.
This can be useful for evaluating combustion performance and identifying opportunities for adjustment, but users should understand what their particular analyzer is calculating.
Combustion efficiency displayed by a portable analyzer is not necessarily identical to the overall thermal efficiency of an entire boiler or heating system.
The analyzer is evaluating combustion-related parameters; the complete system can have other energy losses that are not captured by a portable flue-gas measurement alone.
Read the Measurements Together
The real value of combustion analysis comes from understanding how the measurements interact.
For example, an O₂ reading provides information about combustion air. CO can help identify incomplete combustion. Flue temperature provides information relevant to heat leaving through the exhaust. Together, these values provide a much more useful picture than any single measurement by itself.
The appropriate readings also depend on the fuel, burner, appliance, load and manufacturer’s specifications.
That’s why universal “ideal combustion numbers” should be treated cautiously.
The Right Analyzer Makes Interpretation Easier
Modern combustion analyzers can combine direct gas measurements with temperature, pressure and calculated combustion values, allowing technicians to evaluate equipment using one portable instrument.
The key is selecting an analyzer with the appropriate sensors, measurement ranges and probes for the equipment being tested.
Looking for Combustion Testing Equipment?
Dynamic Agencies supplies combustion analyzers and testing equipment for HVAC, boiler and industrial applications across Canada. Contact our team for help selecting an analyzer for your application.