Wood burning and air quality issues

Residential wood burning releases pollutants into the air just as energy production and traffic do. At the moment, residential wood burning has a different status from other sources of emissions, as it is fairly unregulated in Finland.

Wood burning always generates smoke that contains fine particles, carbon monoxide, hydrocarbons, and other harmful compounds. The more incomplete the combustion is, the more it generates pollutants.

The black or dark grey colour of smoke comes from soot particles. The fine particles that result from wood burning mainly consist of carbon and irritating and carcinogenic condensed hydrocarbons.

Volatile organic compounds, VOCs, are hydrocarbons that smell bad and irritate the airways at low concentrations. Other hydrocarbons, such as benzene and polycyclic aromatic hydrocarbons, known as PAHs, are carcinogenic.

Emissions from domestic wood burning can significantly reduce the quality of air in the surrounding area. This is because they are released into outside air undiluted and unfiltered.

In residential areas with single-family houses, smoke-related problems are at their worst on cold and calm winter days. In winter, people tend to use their fireplaces a lot, and the smoke hangs low due to the weather conditions. The resulting pollutants are transported indoors through ventilation.

Wood burning

You can choose what kind of smoke your chimney spews out. Only burn dry and clean wood in your fireplace.

The emissions from clean combustion are extremely low compared to poorly managed wood burning. When wood is burned cleanly, the smoke is almost colourless. This type of smoke is mostly made up of harmless water vapour.

Clean wood burning 

Clean wood burning starts with the right choice of firewood. Use firewood that has been dried for two summers. Dry wood is light in colour. You can also identify dry wood by the sound it makes: when you hit two pieces of dry firewood together, they will make a sharp noise.

Only burn dry and clean wood in your fireplace. If it is wet, painted, or impregnated, don’t put it in your fireplace. You should not burn waste paper or other rubbish, but you can use a few sheets of newspaper to light the fire.

In addition to generating harmful emissions, waste burning will blacken the furnace and flue with soot. This will negatively affect the heat transfer capacity of the fireplace.

When choosing a fireplace, pay particular attention to efficiency and emission values. In urban areas, well-designed and efficient heat-retaining fireplaces are a good option for heating, as they do not cause that much of a smoke nuisance.

Finland has not yet set official emission limits for fireplaces and stoves. In spite of this, many manufacturers have developed lower-emission fireplaces, and most state their emission levels.

The worst smoke nuisance comes from old-fashioned combination furnaces that have no thermal energy storage. These furnaces often burn firewood slowly. In practice, this means that not enough air is let into the furnace. This type of starved-air combustion generates a lot of emissions.

Remember to get your chimneys swept regularly. Fireplaces and chimneys must be swept once a year in permanently occupied dwellings and once every three years in recreational dwellings. The owner of the dwelling is responsible for ensuring that the chimneys are swept in accordance with the law.

How to light a fire the right way

In terms of emissions, the most critical stages of the combustion process are the ignition and the beginning of combustion. By lighting a fire the right way, you can easily affect the amount of emissions you generate.

  • Before lighting the fire, check that the damper is open and that ashes have been removed.
  • Place the firewood in horizontal layers so that air can flow between the logs.
  • Place the largest logs on the bottom and the smaller ones on top of them, with kindling on top.
  • Leave at least one third of the height of the firebox empty.
  • Make sure that there is enough replacement air coming into the room.

The top-down method has been proven as the best way to light a fire. The heat released by the kindling causes the volatile materials in the firewood to evaporate and ignite, and almost all the vaporised material will then burn. If the kindling is placed underneath the firewood, the wood will be converted into gases, but some of the gases will be released into the air unburned. This method generates a lot of emissions.

Lighting the fire from the top down is the best method for almost all fireplaces. It is always best, however, to follow the manufacturer’s instructions.

To maintain a good combustion temperature throughout the process, the burn rate should be right. If the wood burns too slowly or too quickly, the combustion will be incomplete. The burn rate can be adjusted by controlling the air supply. 

Wood contains 85–90% volatile materials. This is why firewood mostly burns in the form of gases. Wood burning is successful when the wood is converted into gases in the fireplace. Instead of being released into the air as pollutants, the resulting combustible gases burn and release heat. Uncontrolled wood burning usually blackens the fire chamber, furnace door, and flue with soot.