Wood heating: stepping up measures to reduce air pollutant emissions

In France, nearly 7.5 million households use wood for heating. Although it is a widespread energy source considered to be renewable, domestic wood heating contributes to air pollution. ANSES has carried out an expert appraisal on the composition of the pollutants emitted by domestic wood heating systems, their impact on air pollution and their effects on human health. In conclusion, it stresses the importance of continuing and stepping up the measures already taken to better control this source of pollution.

An expert appraisal provided for in the French national action plan to reduce emissions from wood heating

A plan to reduce emissions from wood heating was launched in 2021 by the French Ministry of Ecological Transition, with the aim of lowering annual PM2.5 particulate pollution from this source by 50% between 2020 and 2030. In this context, ANSES received a formal request from the public authorities to improve knowledge on the health impact of particulate matter produced through wood combustion in domestic heating systems used by households (excluding biomass boilers used in multi-dwelling units), such as old or new wood-burning stoves, pellet stoves, open fireplaces, and wood-burning inserts or boilers.

Wood heating is a major contributor to outdoor air pollution

The Agency’s expert appraisal shows that in winter, wood heating is a major contributor to outdoor air pollution for organic particles and a significant contributor for black carbon as well as PM2.5 and PM10 suspended particles.For example, in metropolitan France, over the winter period studied, the average contribution of domestic wood heating was estimated at 77% of the atmospheric concentration level for organic particles, 72% for black carbon and 40% for PM2.5.

While wood heating contributes to indoor air pollution, other sources of emissions, such as tobacco, candles and incense, can generate equivalent or even higher levels of pollution.

Marked regional and sub-regional disparities

Across mainland France, the contribution of wood heating to air pollution varies depending on the region. It is higher in the southern and eastern parts of the country and, more generally, in the coldest areas and regions where the dispersion of pollutants is limited by topography and temperature inversion phenomena, such as in mountain valleys, for example. It is also higher in densely populated urban areas such as the Île-de-France region and particularly Paris, where wood fires, whether for supplemental heating or for leisure purposes, play a major role in outdoor air pollution.

Several factors influence emissions

Many different factors influence emission levels and pollutant concentrations: these include the type of system used, the conditions of use, and the characteristics of the fuel.

Generally speaking, open fires and other older log-burning systems are the biggest sources of pollutant emissions. These emissions are also increased by conditions of use that cause the system to operate outside its optimal range. This occurs, for example, when a system is used at reduced output (low draught) or when the wood’s moisture content is too high or too low, both of which increase pollutant emissions. Conversely, the user’s adherence to the manufacturer’s recommendations for the adjustment, use and maintenance of their system is a key factor in reducing emissions.

Health effects primarily due to older appliances

Pollution from wood heating is associated with effects on respiratory, ENT and cardiovascular health. In particular, it can promote or exacerbate conditions such as asthma and chronic obstructive pulmonary disease (COPD). Certain population groups – such as people with heart or respiratory conditions, children, and individuals aged 65 and over – are more vulnerable.

The observed health effects appear to be mainly attributable to old wood heating appliances and, more generally, to log-burning stoves when used in slow-burning mode (operating at reduced output).

Continuing the measures already taken to control this source of pollution

To achieve the target of a 50% reduction in PM2.5 emissions from wood heating between 2020 and 2030, ANSES recommends that the public authorities step up the efforts that have already been initiated, taking regional differences into account.

It therefore proposes recommendations to supplement those already issued, including those of the French Agency for Ecological Transition (ADEME), to be considered for the next national plan to reduce air pollutant emissions; these include checking the performance of wood heating systems and maintaining it over time, and raising awareness and providing information to users on best practices to limit pollutant emissions.

Addressing all sources of emissions

Lastly, while wood heating is a significant source of air pollution, the Agency points out that it is not the only one. Any lasting improvement in air quality requires addressing all controllable emission sources, particularly those related to road traffic, biomass combustion (agricultural burning, stubble burning, wildfires, and the burning of green waste), the combustion of petroleum products or coal, and agriculture.