Click here for COVID-19 update

What is the CO/CO2 Ratio?

What is CO/CO2 Ratio?

One of the most searched FAQs on our website are the ratio charts for CO/CO2. We thought we’d delve into this subject a bit deeper to help you understand what exactly the CO/CO2 ratio is and how it is calculated.

CO/CO2 ratio is simply measured CO (Carbon Monoxide) divided by CO2 (Carbon Dioxide). Both gases are measured and not calculated when you use our KANE458s.

CO/CO2 ratio indicates:

• How efficiently the boiler is performing
• How clean the boiler is running

For example:

• A new or clean domestic boiler typically displays a ratio under 0.0040
• A boiler needing cleaning typically displays ratio readings between 0.0040 - 0.0080
• A boiler needing major overhaul typically displays a ratio over 0.0080

You can only see this when you perform a combustion test – In fresh air, your analyser displays 0.0000.

In April 2014, the Ratio Test became a requirement of the Benchmark Commissioning Checklist supplied by boiler manufacturers. CO & Ratio measurements needed to be recorded to show a boiler was left in safe and efficient working conditions, following the Gas Safe Register’s newly published technical Bulletin TB143.

Our KANE 458s’ commissioning test procedure provides this test automatically, recording CO/CO2 ratio measurements in both ‘High Fire’ & ‘Low Fire’ settings.

To help you further why not download our CO/CO ratio charts for Natural Gas & LPG, here: and