Depending on the process to be carried out, industrial furnaces ideally operate with stoichiometric air/fuel ratio (also known as ‘correct ratio’), with which we make sure we burn the fuel completely without an excess of air.

For this purpose, it is typically rounded to 10 parts of air for each of natural gas or 25 parts of air for each part of LP gas, in those cases where the process requires it.

We can work with an oxidizing flame and excess air when using drying ovens, or a reducing flame (with excess of fuel), which can be used in some heat treatments and the melting of certain metals.

In this process, excess oxygen in the atmosphere must be avoided and excess fuel used to ensure the presence of zero oxygen. The excess gas is normally burned when leaving the furnace through the chimney and mixes with the oxygen in the environment.

The air/fuel ratio must be monitored frequently to prevent the burners from operating incorrectly and affecting combustion. Another way to monitor air/fuel ratio is by measuring the combustion gases.


Contents on this article: 
Advantages of maintaining correct air/fuel ratio in your furnace
How to measure the air/fuel ratio in your furnaces

Advantages of maintaining correct air/fuel ratio in your furnace

The main benefits of controlling the air/fuel ratio are:

  • Helps productivity
  • Improves product quality
  • Reduction in fuel costs
  • Lower fuel combustion
  • Reduced hazards
  • Pollutants are minimised

How to measure the air/fuel ratio in your furnaces

Periodic review of burner calibration is one of the simplest ways to reduce furnace energy consumption and to ensure an optimized process.

Other things that it’s advisable to measure are:

  • Temperature of the combustion gases in the furnace chimney
  • Percentage of oxygen in the combustion gases
  • Level of oxygen required in the process

Excess air in the combustion gases can be easily measured by monitoring the content present in the chimney with a conventional oxygen analyzer and, for a more complete measurement, CO can be included.

The percentage of excess of air is obtained with the following formula:


At Nutec Bickley we are experts in all types of industrial furnaces, with the most advanced technology and an expert team ready to assist you. Contact us and tell us about your project.

Author: Hilario Zavala

Advanced Firing & Heating Technology

Experts in process for metals: annealing furnaces, aluminium aging ovens, quenching systems and more.

We are experts in Combustion and Control Services for Heat treating industries, we provide: Galvanizing Kettles, Fuel Train, Gas Control Panel and Air Dryers.