Gas
CO / CO₂ ratio
- where
- measured CO (ppm)
- measured CO₂ (%)
Explain this equation
Works out the ratio of carbon monoxide to carbon dioxide in flue gas from analyser readings. Engineers use the ratio as an indication of how cleanly an appliance is burning.
CO is the carbon monoxide reading in parts per million. CO₂ is the carbon dioxide reading in percent. Rising CO relative to CO₂ points to incomplete combustion.
The two readings are in different units, so they must be put on the same basis before dividing. One percent is 10,000 ppm, which is why CO₂ is multiplied by 10⁴. Taking a ratio cancels out dilution by excess air, which lowers both gases in step.
Sense check: 50 ppm CO and 9% CO₂ gives about 0.00056. Doubling the CO doubles the ratio.
Watch out: both readings must be taken from the same sample on the same basis per the analyser instructions. No acceptance limit is built in; check the manufacturer and current guidance.
Enter your values to see the result.
Good to know
CO and CO₂ are converted to equal concentration units before division. Use matching sample basis and analyser instructions. No combustion acceptance limit is supplied.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.