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What should flue gas analyser readings be?


A flue gas detector is a compact tool that calculates and exhibits the combustion outputs from private and commercial fossil-fueled devices. They are accepted worldwide to estimate the ambient condition of air in residential areas. In that case, being a homeowner means consistently estimating the concentration of different gases. At the same time, this would also require modifying burners on a boiler to reach excellent combustion in a living space. This is possible by employing a flue gas analyser. So, this blog will help us understand what should flue gas analyser readings be?

This tool assists in achieving adequate combustion to cut down the discharge of toxins, such as nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and other particulate matter. This is to help maintain excellent combustion. Speaking of flues, check out our blog titled can a boiler flue go through the roof? On the contrary, our qualified engineers provide a flue gas analyser service in London

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We believe that your safety and the safety of your home is of utmost importance during a boiler service or any other gas appliance-related work. Our customer-first approach is what has allowed us to build up a stellar reputation over the last decade. The only way to ensure that your boiler or appliance is functioning efficiently and safely is with regular maintenance and professional servicing, which are usually carried out annually. There are a number of reasons to get a yearly service.


What does a flue gas analyser do?

A flue gas analyser shows the proportion of CO/CO2 in its exit flue and serves two purposes:

  • Appliance Checking – By placing it in a furnace or exhaust fan, one can determine the grades of O2, CO2, CO, and even flue gas conditions. Some flue gas investigators present users with further data such as data reporting, distinct pressure, boiler productivity, and gas assessments.
  • Ambient Air Monitoring – The flue gas investigator also calculates the space air when turned on or evaluated in clean, outdoor air. It lets you maintain the safety and competence of tools such as stoves, ovens, and cookers that blend air and fuel to produce combustion by-products, such as CO.

CO levels

When the status of CO/CO2 is less than 0.004, it shows the heater is working correctly. If it is between 0.004 and 0.008, it implies a possible issue that should require immediate investigation. If the ratio is more than 0.008, the tool has to be examined, scrubbed, and retested. An investigation occurs when the CO levels cross 100 ppm and 200 ppm in oil or coal-fired devices. Similarly, O2 levels must be 3-5% for gas tools and 5-8% for oil and concrete flue instruments. Besides learning what should flue gas analyser readings be, you should also know that readings for gas instruments should be below 200 degrees centigrade and below 300 degrees for grease and solid fuel devices. In case of fires, if the CO levels at 300 mm cross nine ppm, an examination is necessary. If the reading shows CO levels exceeding 35 ppm, prompt action is needed.

What is the ideal CO2 content of flue gas?

Carbon dioxide, or CO2, is a combustion by-product, and its size in flue gas is a crucial indicator of combustion performance. If the production of CO2 is at the maximum with slight extra air, i.e., entire combustion, the flue gas heat losses are at their lowest. The right subject matter of CO2 following combustion is around 10% for natural gas and 13% for flimsier oils. To determine the CO2 examination, one must possess the O2 study by the analyser. It is vital to note that each fuel has a maximum possible CO2 level which is determined by the chemical composition:

  • Light fuel oil: 15.4% by volume CO2
  • Natural gas: 11.8% by volume CO2

Subsequently, do also check out our blogs which offers insight into topics such as do I need a magnetic filter for my boiler? We hope you enjoy reading them as you go along.

As a homeowner, it is essential to understand what should flue gas analyser readings be to troubleshoot inefficiencies and perform routine upkeep. A combustion investigator estimates and provides data based on what occurs following combustion. The ideal CO2 matter of flue gas for a gas stove rests on the burner. The operator specifies the range of acceptable values. However, the value for setting or adjusting is often narrower than the optimal range for certifying and inspection. Generally, the range for CO2 concentration of flue gas is around 8-11% on a premix burner. At the same time, CO2 within permissible limits is usually less than 250 ppm.

What is a normal CO reading?

The moderate level of CO in houses without gas boilers ranges from 0.5 to 5 ppm. The levels close to correctly revised stoves typically lie between 5 to 15 ppm. Those around inadequately regulated ones may be 30 ppm or above.

Since exposure to CO is a popular way of death, it is crucial to understand its normal reading to keep it at an ideal state. CO gas contests with O2 to tie with blood reducing oxygen in the brain. Even less exposure to CO for extended periods affects the brain’s system.

  • Nine ppm is the highest safety level of CO in an indoor environment for 8 hours.
  • A reading that crosses 200 ppm may induce physical signs in a few hours.
  • Exposure to CO at 800 ppm or greater levels in the air is deadly within minutes.

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Hopefully, this blog helps you understand what should flue gas analyser readings be. The ideal CO content in a flue gas should be below 100 ppm air-free, although the permissible limit in the stack is 400 ppm air-free. If the CO rises and becomes unstable between 1 ppm and 400 ppm during the combustion process, the heater should be turned off or sent for testing and repairs. At the same time, blogs such as the one on what is a zoned heating system? Learn more about it by visiting the link. You should take the necessary steps to ensure the readings of your flue gas analyser are correct.

Can you control CO exposure?

Fortunately, it is possible to decrease exposure to CO by supporting and correcting the combustion equipment. Here are some steps you can take to lessen your vulnerability to CO:

  • Properly adjust all the gas instruments.
  • Employ the right fuel in kerosene heaters.
  • Always open the flues while utilising fireplaces.
  • Establish an exhaust fan above the gas stove.
  • Replace the unvented radiator with a vented one.
  • Select wood kilns meeting EPA radiation requirements.