Air & Fuel Calculators
Actual Air Requirement Calculator
Calculate the actual air a burner should be supplied, combining theoretical air requirement with an excess air margin.
Air-Fuel Ratio (AFR) Calculator
Calculate the air-fuel ratio (AFR) from the mass of air and fuel supplied to a combustion process.
Combustion Air Flow Calculator
Convert combustion air mass flow rate into volumetric flow rate using air density, for fan and duct sizing.
Combustion Air Velocity Calculator
Calculate combustion air velocity in a duct from volumetric flow rate and duct cross-sectional area.
Excess Air Calculator
Calculate excess air percentage from actual and theoretical air supplied to a combustion process.
Fuel-to-Air Ratio Calculator
Calculate the fuel-to-air ratio (FAR), the reciprocal of AFR, from fuel and air mass supplied to a combustion process.
Primary Air Calculator
Calculate the primary air portion of total combustion air supplied for ignition and initial combustion.
Secondary Air Calculator
Calculate the secondary air portion of total combustion air, the remainder after primary air is accounted for.
Stoichiometric Air Requirement Calculator
Calculate the exact stoichiometric air requirement for complete combustion from a fuel's carbon, hydrogen, oxygen, and sulfur content.
Theoretical Air Calculator
Calculate theoretical combustion air from fuel mass and a known stoichiometric air-fuel ratio.
Getting the Air-to-Fuel Balance Right
Every combustion process needs the right amount of air to burn fuel completely — too little air leaves unburned fuel and dangerous carbon monoxide, too much wastes energy heating excess nitrogen that does nothing useful. Ten calculators here cover the stoichiometric and excess air math that boiler, burner, and furnace engineers use to tune combustion air supply.
Popular Air & Fuel Calculators
Ten tools span theoretical air, excess air, and air flow measurement:
- Stoichiometric Air Requirement Calculator — calculates the exact air needed for complete combustion from a fuel's ultimate analysis.
- Excess Air Calculator — finds the percentage of air supplied beyond the stoichiometric requirement.
- Air-Fuel Ratio (AFR) Calculator — calculates the mass ratio of air to fuel supplied to a combustion process.
- Combustion Air Flow Calculator — converts a required air mass flow into a volumetric flow rate for fan and duct sizing.
- Primary Air Calculator — estimates the air introduced directly with the fuel for ignition and initial combustion.
Why Excess Air Is a Deliberate Design Choice, Not Waste
Running a burner at exactly the stoichiometric air ratio is impractical in the real world, because imperfect mixing means some fuel would go unburned without a safety margin of extra air — this is exactly why boilers and furnaces are deliberately operated with 10–20% excess air (sometimes more for solid fuels), trading a small efficiency penalty for reliably complete combustion. Too much excess air, though, carries a real cost: every bit of extra nitrogen swept through the furnace absorbs heat and carries it straight up the stack, which is why excess air percentage is one of the first things a combustion tune-up checks.
Frequently Asked Questions
What's a typical excess air percentage for a well-tuned burner?
Natural gas burners often run efficiently at 10–15% excess air, while solid fuels like coal or biomass typically need 20–40% due to less uniform mixing.
Explore More
Need the flue gas side of the same combustion process? See the Flue Gas Calculators, or check overall combustion efficiency in the Heat & Energy Calculators.