What a Combustion Report Shows, and How to Read One
A tune-up should leave a record. Without readings, there's no way to tell what was adjusted or how far the burner has drifted since the last visit. A combustion report is that record: analyzer readings taken before and after adjustment, at each firing rate.
What a report should include
Equipment: boiler and burner make, model and serial number, the fuel, and the controls in use.
Conditions: the date, the firing rates tested, and fuel pressure at each rate.
Readings at each firing rate, before and after: O2, CO, CO2, stack temperature, combustion air temperature, combustion efficiency, and draft.
Safety checks: which limits, switches and flame detection devices were tested, and the results.
Notes: anything found that needs repair or follow-up.
How to read the numbers
O2 is the oxygen left over. High O2 means extra air is carrying heat up the stack. Low O2 can mean the burner is short on air. More on that in Excess Air and O2.
CO is a product of incomplete burning. It should stay low at every firing rate. CO rising as O2 drops shows where the air was cut too far.
Stack temperature is the temperature of the flue gas leaving the boiler. If it climbs over time at the same load and O2, it can point to soot or scale on the heat transfer surfaces.
Combustion efficiency is calculated by the analyzer from O2, stack temperature and combustion air temperature. It counts heat lost up the stack, not other losses, so it is not the same as overall boiler efficiency.
Why before-and-after matters
The before readings show how far the burner drifted since it was last set. The after readings become the baseline for the next visit. Kept year to year, they show how fast a burner drifts and whether something is changing, such as stack temperature creeping up.
Readings at one firing rate aren't enough. A burner can be set correctly at high fire and well off at low fire, which is why a combustion tune-up covers the full range.
Every tune-up and startup we do ends with a written report showing O2, CO and efficiency before and after at each firing rate. Request service or email service@combustionspecialists.com.
