Boiler Combustion Efficiency Calculator
Calculate excess air from stack flue gas oxygen, sensible stack losses, fuel moisture losses, and monetary savings from tuning burner air-fuel ratio.
Fuel & Flue Gas Parameters
Boiler Firing & Fuel Economics
Combustion Efficiency & Air Ratio
Heat Loss Breakdown (ASME PTC 4.1)
Burner Tuning Savings Potential
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
What is the relationship between stack O2 and excess air in a boiler?
Excess air is the volume of combustion air supplied beyond stoichiometric requirements. Flue gas oxygen percentage directly indicates excess air via the formula Excess Air % = [O2 / (20.9 - O2)] × 100. For natural gas, 3.0% O2 corresponds to roughly 15% excess air, which is considered optimal for modern commercial burners.
Why does excessive excess air waste fuel in steam boilers?
Every pound of unnecessary ambient air drawn through the burner absorbs valuable combustion heat and carries it straight out the exhaust stack into the atmosphere as sensible dry gas loss. Reducing excess air decreases stack gas volume, directly increasing thermal transfer into boiler tubes.
What are the dangers of reducing excess air too low?
If excess air falls below stoichiometric requirements or burner air-fuel mixing is uneven, incomplete combustion occurs. This generates poisonous carbon monoxide (CO), dense unburned soot, soot deposits on heat exchanger tubes (which act as thermal insulators), and potential explosion hazards in the flues.
What is the difference between combustion efficiency and thermal efficiency?
Combustion efficiency measures how completely the burner extracts chemical energy from the fuel into heat (flue gas stack loss + moisture loss). Thermal efficiency (or fuel-to-steam efficiency) also accounts for shell radiation, convection, and boiler water blowdown losses.