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Adjusting the Stoker Burner


On the left side the heart of a new heating system. This is where the adjusting happens. On the right side old-fashioned control centre.

The results of adjustment do not show immediately, so reserve plenty of time for the adjusting process. Wait a few hours between the adjustments so that the burning has steadied. Carefully done adjustments pay off later.

The burner can be adjusted relatively well at home. If very accurate results are desired, there are special purpose-built gauges and analysers that indicate the levels of carbon dioxide (CO²), oxygen (O), and carbon monoxide (CO).

Flame and Smoke Colour

By following the colour of flames and smoke, the stoker burner can be adjusted to burn as purely as possible. The colour of the flame depends on the fuel and its moisture content, and the temperature in the burner. When the burning is clean, the colour of the flame is white and yellow and the smoke coming from the chimney is light grey. In the summer the smoke should be almost invisible or very light grey.

When moist fuel is burned, the smoke can be really thick and yellow in colour. The burning is then incomplete, and combustion gases run unburned out of the chimney. Poorly adjusted system requires sweeping constantly, but when the adjustments are properly done, sweeping only few times per month is enough.

Practical tips

Below are listed some observations and advice about adjusting a stoker burner, based on personal experience. They can be applied also to dry firewood burning.

The flames are red and there are black spirals among the flames. The boiler gets sooty and black or dark smoke comes out of the chimney.

  • There is not enough secondary air.
  • Add secondary air, but not so much that unburned fuel flies out of the burner. If this happens, reduce fuel feed.

The flames are white or bluish, restless or glaring, and chimney smoke is white.

  • Reduce secondary air until chimney smoke is light grey.

The temperature of combustion gases should be over 150 Celsius degrees. Even though the efficiency might be higher with lower combustion gas temperature, there are other downsides. Unburned gases might escape out of the chimney. Water can condense of the combustion gases on the boiler and chimney surfaces, which erodes them.

However, the combustion gases should not be over 250 Celsius degrees. Temperature this high tells that the boiler efficiency is not right. It has to be noted that with biofuels more combustion gases are produced than when oil is burned.

Well-burned fuel leaves a thin layer of ash on the fire surfaces, the colour of brown or grey depending on the fuel used. The layer falls down by itself, which easies the process of sweeping and lessens the sweeping times needed. This means that the adjustments are right.

Adjusting a modern stoker burner is as easy as adjusting an electric oven (in the picture).

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