Carbon Monoxide, Combustion Analysis, and Indoor Air Quality
Domain 8 focuses on carbon monoxide, combustion analysis, and indoor air quality. The exam tests CO formation, exposure limits, analyzer interpretation, and ventilation. CO is colourless, odourless, and lethal; a clean flame does not guarantee safe flue gases.
CO and combustion analysis
CO forms when there is incomplete combustion: insufficient air, poor mixing, flame impingement, blocked flue, or over-firing. A combustion analyzer measures O2, CO2, CO, and stack temperature. Calculate CO/CO2 ratio by dividing CO ppm by CO2 ppm; a rising ratio indicates deteriorating combustion. Also measure draft and ambient CO.
Indoor air quality
Ventilation must replace exhausted air. Depressurization can spill flue gases from natural-draft appliances. CO alarms should be installed per the manufacturer and local code, not used as a substitute for combustion analysis.
Worked example
A natural-draft boiler shows 80 ppm CO and 10% CO2. CO2 = 100,000 ppm, so CO/CO2 = 80/100,000 = 0.0008, which is low. Another boiler shows 600 ppm CO and 8% CO2: 600/80,000 = 0.0075, five times higher. You investigate air supply, burner alignment, and draft before condemning the appliance.
Traps
- Treating a CO alarm as the only test.
- Measuring CO before the appliance stabilizes.
- Ignoring ambient CO or back-drafting.
- Assuming high CO2 always means high efficiency without checking CO.
- Using an uncalibrated analyzer.