Combustion Efficiency – An Application Guide for Thermal Mass Flow Meters

Combustion is the process of burning fuel in the presence of oxygen. The fuel, often natural gas is a hydrocarbon, and air supplies the oxygen. During this reaction, carbon dioxide and water are formed, and the heat is given off. Thermal mass flow meters measure air and natural gas flow rates to provide optimum combustion.

Combustion Efficiency

Combustion efficiency can be created when measuring air flow and natural gas flow with thermal mass flow meters to a device.
Questions about using a thermal mass flow meter in a combustion efficiency application? Call (831) 242-2030 or email

Combustion efficiency depends on the air-to-fuel ratio. Incomplete combustion will occur if there is too little oxygen to react with all the carbon in the fuel. In this case, there is a reduction in combustion efficiency as unburned or partially burned fuel (carbon monoxide) is discharged.

Complete combustion occurs when there is sufficient oxygen to react with all the fuel. Perfect combustion occurs at stoichiometric conditions where all the fuel burns with all the available oxygen. In reality, complete combustion takes place when some excess oxygen is present. However, too much excess oxygen results in the excessive discharge of heat which reduces combustion efficiency.

By measuring and controlling the fuel flow and the air flow, we can create the most efficient operating conditions for complete combustion.

Measure Natural Gas

The flow of natural gas to a combustion source is easily measured using a thermal mass flow meter. This gas often flows in 1-inch to 6-inch pipe. In-line flow bodies can be used for pipe sizes up to four-inch, and insertion style probes are suitable for one-inch pipe and larger.

Measure Air Flow

The amount of air is roughly ten to twelve times the amount of natural gas consumed. Fans supply the air, and ductwork directs the air to the combustion burner. It is easy to install thermal mass flow meters with insertion probes through the wall of the ductwork. For large ductwork, consider multiple probes to account for variations in the flow profile.

Thermal Mass Flow Meters

Advantages of thermal mass flow meters for determining the air to fuel ratio are:

    • Direct mass flow measurement without pressure and temperature correction
    • Virtually no pressure drop
    • High rangeability
    • High accuracy
    • Very reliable

A way to reduce energy use in an industrial environment is to optimize the combustion efficiency of heating sources. Read more about how thermal mass flow meters assist in achieving combustion efficiency and energy management in the Sage Metering white paper, “Combustion Efficiency and Thermal Mass Flow Meters.”