Does heating with wood pollute more than driving a diesel car?

Illustration: Energy Revolution, Getty/Canva.

Using wood to heat your home has particular financial advantages in the context of the energy market crisis. However, burning wood releases a large amount of fine particles into the atmosphere, becoming the first source of this pollution in the city as well as in rural areas. However, good practices in the use of wood heat can reduce emissions.

With rising energy prices, the French are in favor of heating with wood. Fuel supply difficulties reported by some suppliers since September reflect this enthusiasm for the sector.

New buildings are increasingly equipped with wood heating. But not only. Renovating older homes often involves using wood to replace outdated heating systems. Wood boiler, inserts, wood or pellet stoves. The options vary depending on the characteristics of the residence and the needs of the residents.

By using wood for heating, we think we are doing something for the planet because wood is a natural material. But that’s not entirely true, or at least not as true as you might think. A recent article in La Tribune highlighted that wood burning emits more fine particles than diesel cars. This is a reality.

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The smoke produced by burning wood consists of various pollutants, especially fine and very fine particles. Thus, wood heating in the residential sector is responsible for 43% of national PM2.5 emissions, i.e. small particles no larger than 2.5 microns in size. It is also the source of more than half of PM1 fine particle emissions, according to the Ministry of Environmental Transition. Remember that the finer the particles, the easier and deeper they penetrate into our body.

Other pollutants such as carbon black, benzene, benzopyrene, carbon monoxide and nitrogen oxides are also found in smoke from chimney fires. It is on this basis that in July 2021 the government published an action plan aimed at halving fine particulate emissions from domestic wood burning.

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Because, according to Santé Publique France, fine particles cause 40,000 deaths a year in France, which shows the need to inform consumers about the conditions of using their fireplaces. Moreover, since 2015, open fireplaces, which are more polluting and less efficient, have been banned in Paris and around 400 cities in Ile-de-France. The Que Choisir association already warned in 2019 that heating in an open fireplace emits particles as fine as a diesel car that has traveled 3,500 km.

On its website, the Airparif observatory shows that burning a chimney in an open fire is equivalent to the emissions of a diesel car that will travel about 7,000 km. However, the duration of the chimney fire in question is unknown. The government mentions this in its action plan “Open fireplaces are responsible for 21% of total emissions from wood heating, while they account for only 10% of the national appliance fleet”. Therefore, although this equipment is very inefficient (15% efficiency maximum), it pollutes more.

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How to reduce fine particulate emissions?

Therefore, the government mentions some details about wood heating in its road map. It is important to use “new device of correct size and well maintained”. It is also necessary to use good quality, very dry fuel (moisture below 20%). Indeed, the use of wood with a moisture content of less than 20% allows to reduce PM2.5 emissions by 75% compared to 30% wet wood, again according to the Ministry of Ecology.

Finally, to avoid idling and therefore poor combustion in inserts and wood-burning stoves, the “top” ignition mode should be preferred. This reverse kindling consists of first placing large logs inside before building up different layers of progressively thinner wood.

A fire extinguisher (ideally wood fiber) is placed just below the last branches of the tree. Thus, the fire will spread from top to bottom. This ignition mode significantly reduces particulate-laden smoke. This is important when you know that 80% of pollutants are released at the start of the ignition cycle, within the first 10-15 minutes. For the government, following these good practices would allow fine particle emissions to be divided by 10.

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By 2025, 600,000 devices will need to be replaced

To encourage consumers to pollute less with wood heating, the government is encouraging the replacement of older appliances with more efficient models. Aid schemes for energy renewal, such as Ma Prime Rénov, are dedicated instruments for this action plan. The original goal was to replace 600,000 devices by 2025.

Finally, is it good to heat the planet with wood? According to Que Choisir, all three of the highly polluting outdoor fireplaces and inserts should be avoided in favor of efficient and less polluting mass furnaces, pellet stoves and wood boilers. You can certainly keep your supplement, but you should be careful to use it properly by following the precautions mentioned above.

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