Flue gas is a term that refers to the gas emissions generated during the combustion process. These gases are emitted through buildings' chimneys or flues. Combustion is a process that involves the mixture of fuel and oxygen, both being entirely consumed in the burning process. The perfect circumstances would provide enough air in the combustion chamber to ensure the complete burning of the fuel. It could happen if it were physically possible to bring each atom of fuel in direct contact with the amount of air needed to complete its combustion. But so far, there is no method that could enable this.

In the past, the flue gas analysis was a very lengthy process and was also quite pricey. Today, however, as technology progresses, we have cheaper and easier methods. Testo is one of the brands that offer excellent devices that will help you measure, analyse, and document glue gas and determine if combustion systems are working at the optimum settings and meeting environmental compliance. Besides Testo thermometer devices for analyzing gas, you can also find many other devices that will help you with your work such as smart tools refrigeration sets or digital vacuum micron gauge with Bluetooth.

Testo measuring tools

How It Works


Flue gas analysers are used to measure the emissions of household appliances and control their safety. These devices work by determining how much harmful gas the appliances produce. Flue gas typically consists of Nitrogen, Carbon dioxide, water vapour, Sulfur, Oxygen, dust, soot, Carbon monoxide and other pollutants. Of these emissions, the most dangerous and harmful one is carbon monoxide which has no colour or odour, meaning it's difficult to detect and large amounts of it can kill a person in no time. The flue gas analyser is an excellent device that can help you detect the risk of leaked carbon monoxide by monitoring ambient air.


To test an appliance, make sure to put the probe of the analyser in the exhaust of the appliance you're measuring. The sensor will detect gas emissions that the appliance releases and the results will show on the digital screen, letting you know about any risk of poisoning and the efficiency of the appliance as well.  Controlling ambient air is similar to calculating flue gas measurements but instead, you should conduct a combustion analysis in open air. A flue gas analyser is a helpful measuring instrument for assuring that the air in a building is safe. Some gases, like carbon monoxide, can be fatal (in large amounts), which is why these gases must be caught in the open air as soon as possible. Be sure to get the right Testo devices such as the Testo flue gas analyzer, Testo thermometer, refrigerant leak detector and so on.

How to Take Gas Samples Testo


How to Take Gas Samples


Flue gas analysis is done by inserting a probe into the flue of the boiler. Place it between the last heat exchanger and the draft diverter. This also known as 'in-situ' testing is necessary to take a combustion air temperature measurement. But, not all analysers use ‘in-situ’ probes. You will find units that pump flue gases through a tube to the instrument which is more typical of constant monitoring equipment. The same goes for large systems where it's not easy to reach a spot in the flue to insert a probe or locate a portable matter.

The first thing to do when taking a gas sample is to make a little hole in the flue pipe (it's sized to fit the problem closely without air leaking). To get an accurate measurement, the gas-sampling probe must be set before any draft damper or diverter. This way the gases are not diluted and are as close to the equipment breach as possible (the gases are not cooled in the flue this way). If you have a stack economiser or similar device, the measurement should be performed downstream of the installed device. It is important to remember that to have the most accurate measurement there should be no gas leaks.
Make Temperature Measurements
To make temperature measurements, the thermocouple probe should be placed at the point of the highest exhaust gas temperature at the base of the flue and toward the small duct centre. If the stack gas temperature is underrated, the operating efficiency will be amplified.

Take O2 Measurements

Take O2 Measurements


Once you have calibrated the instrument used to measure O2 levels, it's important to put the analyser where the emissions are discharged, normally the stack. Begin the combustion process and check for stability in the oxygen readings for about one to three minutes.

Soot, Smoke & Particulate Measurements


When the equipment is tuned up and maintained, the most commonly measured thing is soot. This is done by extracting a sample of the exhaust gases by using a manual sampling pump or special soot probe. The sample is always taken from the same location as the stack temperature measurements. These measurements may be performed with smoke pumps or with probes with filters.

Keep Records


It's essential to document your measurements to ensure a short and long term understanding of the combustion process. This way you can compare previous and today's data and identify the components of the combustion system that justify replacing that will maximises the combustion efficiency of the process. Gas analysers that come with built-in printers and/or data logging capabilities give the best methods of data storing and record keeping.

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