Combustion Analysis

Do you think your furnace is running at its maximum efficiency? Want to know for sure? Call Michael Bonsby Heating & Air Conditioning! Our expert HVAC technicians can run a combustion analysis on your furnace and help you figure out exactly where it’s losing efficiency – and what you can do about it!

A combustion analysis is basically a measurement of your system’s flue gases to determine the completeness of the combustion process. Fuel combustion is the first step toward maximizing your furnace’s fuel efficiency, and as a result it’s extremely important to fully understand it before your furnace is fully installed.

The Basics of Combustion Analysis

Before we start talking about combustion analysis, we need to spend some time talking about air. Air for combustion is divided into four types: primary air, secondary air, excess air and dilution air.

• Primary air provides a percentage of the combustion air. More importantly, however, it controls the amount of fuel that can be burned.
• Secondary air improves combustion efficiency by allowing the fuel to burn completely. Normally, power burners won’t require secondary air. However, air leaking in via access doors, burner mounting flanges, boiler sections, etc will dilute the flame and flue gas temperatures, reducing operating efficiency and making it more difficult to monitor combustion conditions.
• Excess air is air supplied to the combustion process to ensure each molecule of fuel is totally surrounded by combustion air. A furnace tune up will improve the flow of combustion air, reducing the need for excess air.
• Dilution air is required in order to control stack draft, which will reduce efficiency-inhibiting condensation from forming in your vent system.

Now, most furnaces use either natural gas or propane to create heat, both of which are made up mostly of carbon and hydrogen. Basically, the more hydrogen the fuel has, the more excess air it’s going to need. The excess air combines with the oxygen from the combustion air to create perfect, efficient combustion. Too much or too little fuel combined with the available combustion air could result in unburned fuel and inefficient heating at best and, at worst, carbon monoxide production!

Combustion Analysis for Efficiency

When we talk about a furnace needing to be “properly installed” in order to be as efficient as possible, we mean it has to be installed with special consideration paid to combustion analysis. As you may know, every furnace comes with an AFUE rating – annual fuel utilization efficiency. This is the maximum rating possible for a specific furnace. The only way to tell the actual fuel utilization rate of your specific furnace is by performing a combustion analysis!