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Combustion Analysis—An Essential Part of Boiler Maintenance

A boiler is a complex piece of equipment. While some diagnostics can be done by observation, a detailed understanding of a boiler’s operation can be diagnosed through a combustion analysis, similar to your family doctor ordering “a complete blood-workup” with your annual physical.

Combustion occurs when fossil fuels react with oxygen in the air to produce heat. When fossil fuels are burned, the principal chemicals produced are carbon dioxide and water. When combustion is not properly controlled, other chemicals are often formed including carbon monoxide and nitrogen oxides, as well as soot.

A combustion analysis measures the air-to-fuel ratio of the burner to help determine boiler efficiency and also may identify emissions output from the boiler.


Three Reasons to Perform a Combustion Analysis

  1. Energy Efficiency
    • The largest source of boiler heat loss is due to heat leaving the system through the system exhaust (stack).

  2. Reduced Emissions
    • Carbon monoxide and nitrogen oxides are toxic emissions governed by federal and state environmental agencies such as the EPA.

  3. Safety
    • Toxic and potentially explosive gasses can build up in the stack or become vented back indoors. Not only do these present potential safety hazards, they also significantly reduce boiler efficiency.

Two Components of a Combustion Analysis—What Is Measured and Why?


1. Stack Gasses—Ideally the only exhaust gasses should be water vapor, carbon dioxide, and nitrogen. Carbon monoxide readings are usually the result of not enough air being supplied to the burner or low flame temperature. Nitrogen oxides can be the result of oxygen combining with the air or the fuel, potentially a poor air/fuel mixture. Volatile organic compounds (VOCs) are generally the result of incomplete combustion requiring burner maintenance and/or improper air/fuel mixture. Soot is commonly also caused by low flame temperature, or poor air/fuel mixtures.

2. Temperature and Draft—Too much heat leaving the stack becomes a major source of lower fuel efficiency. Generally speaking, fuel efficiency drops as the exhaust temperature increases, but the temperature in the stack needs to remain high enough to avoid condensation inside the stack, which can cause acid and damage the system. High temperature readings could be caused by a combination of dirty heating surfaces, water scale build-up, or excessive velocity of water inside the boiler. Draft (the gas velocity through the boiler), measured by the pressure in the stack, also needs to be balanced. Too much draft can pull the flue gasses through the boiler too quickly, preventing effective heat transfer to the system and lowering efficiency. However, low draft pressures can cause temperatures in the stack to decrease, again causing condensation.

Service Matters: Boiler Gas
When and How Often You Should Perform Combustion Analysis

It is good practice to perform a combustion analysis after cleaning or replacing the blower wheel, or replacing the blower motor, gas valve, or gas pressure regulator.

Most boiler manufacturers today recommend an annual combustion analysis as part of routine boiler maintenance. In addition, it is good practice to do a combustion analysis after cleaning or replacing the blower wheel, or replacing the blower motor, gas valve, or gas pressure regulator. Because it is necessary to operate the boiler for at least 15 minutes prior to making any adjustments in order to let the flame stabilize, it is best to perform a combustion analysis when the building is under a heavy load, such as in mid-winter.

We can help. Speer Mechanical is an ongoing mechanical service and maintenance provider to building owners throughout several states for routine, contract maintenance and emergency service.

Need more information?

Jim Hangen 614.261.5149

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