What is a Combustion Efficiency Test?

Any time a technician services your heating equipment, they’ll perform what’s called a combustion efficiency test. Combustion efficiency tests measure how effectively your heating system is converting fuel into heat. These tests reveal to the technician if they’ve set up the burner correctly. They also help improve your system’s efficiency, which saves you money.


A certain amount of air must be supplied to completely burn fuel. Inadequate amounts of air will result in unburned combustibles, like smoke, fuel, soot and carbon monoxide, whereas too much air will result in heat loss due to an increased flue gas flow, which lowers efficiency. Operating your equipment with the right amount of excess air will keep heat loss to a minimum and improve combustion efficiency.


There are three things a technician can adjust on your equipment that will impact the combustion process: fuel pressure, combustion air and draft. To carry out the test, technicians can use manual or digital electronic instruments. Manual instruments can be time-consuming to use and may not yield the best snapshot of the burner performance because a manual test culminates in a single reading. Digital equipment, on the other hand, automatically calculates efficiency and samples continuously, enabling the technician to get a better feel for how results are changing.


A typical procedure will cover these areas:


  • Test the stack temperature, or the temperature of the combustion gases leaving the appliance, which reflects the energy that did not transfer from the fuel to the heat exchanger.
  • Test for draft, or the flow of combustion gases and air through the burner, heating unit and venting system.
  • Test for smoke concentrations in the flue gases. The technician will adjust the burner to create a flame that produces as little smoke as possible, as keeping smoke to a minimum is critical for high-efficiency operation.
  • Test the temperature and composition of the flue gases, or excess air, CO2, O2, and NOx.
  • Calculate the efficiency. If your heating equipment’s combustion efficiency is below 78, you may want to consider an upgrade, as a new burner will burn the mixture of fuel and air in a cleaner and more controlled manner, resulting in lower heating costs.


If you think you may need service on your equipment, contact us and we’ll send over an expert technician to take a look.

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