Combustion Analysis: What You Need to Know

If you're running boilers and you're not doing combustion analysis, you're guessing. That's not a judgment — it's just the reality of the work. Combustion analysis tells you what's actually happening inside the firebox. Everything else is inference.

What Combustion Analysis Actually Measures

The fundamentals: O2 or CO2 concentration, CO (carbon monoxide) in the flue, flue gas temperature, combustion efficiency percentage, excess air. Put those numbers together and you know whether your burner is operating efficiently, whether you have a draft problem, and whether you're producing dangerous levels of CO.

You cannot get this from looking at a flame. You cannot get it from sound. You need the numbers.

The Fieldpiece SOX3

This is the analyzer I recommend for stationary engineers and boiler operators. The SOX3 measures O2, CO (with hydrogen correction), flue temperature, and calculates efficiency and CO2. It's probe-and-display design, built for field use, and Fieldpiece has a strong track record in commercial HVAC and boiler work.

When to Run Analysis

At startup every season. After any burner adjustment. After a nozzle change. After any work on the combustion air system. And periodically during operation — monthly at minimum on high-use systems. Document your readings. Trend lines tell you things individual readings don't.

CO Is the Number That Matters Most

Efficiency is important. CO is critical. Elevated CO in the flue means incomplete combustion. It means carbon monoxide production. On a properly sealed system it vents safely — but "properly sealed" is the variable you need to verify. Know your CO readings, know your thresholds, know your local codes.

For the broader stationary engineering context — licensing, exam prep, operational standards — the full guide is in the book.