5 Reasons Why Combustion Analysis is Important

This post covers 5 Reasons why combustion analysis is important for fossil fuel heating equipment in homes.

Combustion analysis is the act of testing the combustion process of your furnace or boiler. This is done by sampling the gasses in the flue piping with a tool called a combustion analyzer. Testing is usually performed during the installation and commissioning of new equipment and systems. However, combustion analysis should continue to be performed on a periodic basis, like during a boiler maintenance. This is especially the case when a component impacting the combustion process has been repaired or replaced. Moreover, it is important to remember that consistent normal readings are more meaningful than an isolated normal reading.

For combustion to take place, 3 things are required: heat, oxygen, and fuel. These elements cannot be arbitrarily mixed. For combustion to be safe and efficient, there must be a proper amount and combination of each introduced to the burner. A burner and flue system must be calibrated to combine the proper quantities of each element for the proper mixture.

Combustion analysis is important for 5 main reasons as briefly discussed below.

The 5 Reasons Why Combustion Analysis is Important for HomeOwners


The safety of a boiler or furnace can be checked by performing a combustion analysis. Several aspects of the combustion can be checked. For example, draft readings can tell you if there is proper draft to carry the combustion gasses out of the house. Readings can be taken over the fire and in the stack to determine whether an obstruction exists. In addition, a stack temperature reading can let you know if the flue is running too hot. Both readings can be informative on whether unsafe gasses are entering the house when improper combustion is producing elevated levels of carbon monoxide (CO).

Efficiency & Comfort

Optimal efficiency and comfort is achieved when the proper amounts of fuel and oxygen are combined at the burner and the flue is operating normal. Your furnace or boiler is not efficient if it is burning too much fuel or is taking in more air than is recommended or required. Likewise, it is inefficient if less than required amounts of fuel or air are being delivered. An improper mixture of elements will cause improper readings.

Combustion readings will provide information on the levels of the byproduct gasses and thereby allowing for adjustments to the amount of fuel and air. Adjustments may be more difficult depending on the type of system you have. And its important to remember that making one adjustment may cause having to make further adjustments on other components on the system.

Knowing the impact each adjustment will have on other readings and what low and high level combustion readings mean, make combustion adjustments easier. A technician properly trained in combustion analysis will have a good sense of what adjustments are required when certain readings are not within normal range.

Minimizing pollution

In jurisdictions that regulate pollution levels from combustion, levels of byproduct gasses are measured to comply with local code. Analyzers measure the level of Nitrogen Oxides NOX and Sulfur Oxides SO2 that exist in the flue gas.

Technology exists that reduces the amount of these pollutant byproduct gasses. Manufacturers have certain models and options that reduce the amount of excess air or flame intensity thereby reducing the amount of these gasses being produced and expelled into the ozone. The downside to taking measures to reducing these pollutant gasses is that increased levels of carbon monoxide can occur at least when reduction of intake air is the method being utilized.

Adhering to manufacturer’s specifications

There are known “typical” combustion readings that are published and act as good guidelines. These typical readings are given for the type of fuel, equipment, and flue being used. In most cases, these guidelines should be followed.

They should not, however, be followed in cases where the manufacturer’s specifications vary. It is always important to consult with the literature that came with the equipment so that the correct adjustments are made if required. This is also important to comply with the warranty requirements.

Improving longevity

A combustion reading can tip you off on whether conditions exist that can have an impact on the longevity of the furnace or boiler. There are several conditions that can cause harm. Some conditions, if allowed to go unchecked for too long, can cause early failure.

One catastrophic failure is when the heat exchanger in a furnace develops cracks and leaks. When this happens, the heat exchanger or furnace itself must be replaced for safety reasons. A cracked heat exchanger can either cause carbon monoxide to enter the home or a flame rollout condition due to a pressurized combustion area. In either case, the conditions are not safe for occupants and the structure. A combustion analysis could have recorded readings indicating conditions that caused this failure. (eg. – bad draft, high draft temperatures). A crack could be shown by increased levels of O2.

A combustion analysis can also tip you off that equipment is creating excessive soot or that the system may have soot buildup that needs cleaning. Excessive soot on the heat exchanger can hold moisture and start developing pitting compromising the metal.

An analysis can also indicate a lack of dilution air which means the system has been operating and creating condensation in the flue pathways. This can lead to short lived flues and flue liners from corrosion and deterioration.


The purpose of this article was to provide a very brief non-technical resource about combustion and the importance of measuring and analyzing it. There is a real necessity for analyzing combustion in residential settings with furnaces and boilers. Homeowners, technicians, the environment, and the equipment can all benefit. Please pass this post along to friends and family so they are aware of the 5 reasons why combustion analysis is important.

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