Dr Éric Thorin, Ph. D.

Professeur titulaire, Département de Chirurgie, Université de Montréal. Chercheur au centre de recherche de l'Institut de cardiologie de Montréal.

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Dr Martin Juneau, M.D., FRCP

Cardiologue, directeur de l'Observatoire de la prévention de l'Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention Watch, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.

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6 January 2026
Residential wood burning: A major cause of air pollution

Overview

  • When discussing pollution as a health risk factor, ambient air pollution from wood fires is considered to be the leading cause of premature death in Quebec, far ahead of pollution related to road transportation.
  • Fine particles, when acting in synergy with the gases and volatile organic compounds produced by wood combustion, are the most toxic, as they accumulate in the body without being eliminated effectively. Over time, this creates chronic inflammation that promotes the development of chronic lung and cardiovascular diseases, as well as cancers.
  • New generation wood stoves, even if certified, remain significant sources of contaminants, generating fine particles well beyond tolerated thresholds.

Air pollution is not a recent phenomenon: it began when humans started burning materials for cooking and heating, primarily wood, and more recently, fossil fuels.

The World Health Organization (WHO) has defined air pollution as a major contributor to disease and premature death, and as the most significant environmental risk factor for human health. A 2018 review summarizing WHO data estimated that 9 million deaths are directly attributable to environmental pollution (Fig. 1) and 2.9 million to indoor air pollution. These figures were extensively updated by Max Roser in 2021, who estimated that between 2.3 and 3.8 million premature deaths worldwide are linked to indoor air pollution.

Figure 1. The contribution of air pollution versus other risk factors to global mortality. Adapted from Landrigan et al. (2018).

What about in Canada and Quebec?

In its 2021 report, Health Canada estimated, using scientific data modelling, that in 2015, air pollution associated with residential wood burning caused 2,300 premature deaths. In Quebec, this figure is estimated at 1,400 premature deaths, representing 60% of Canadian deaths. Air pollution from road transportation is the second leading cause, estimated to have caused 400 premature deaths in Quebec. By comparison, the number of road traffic fatalities in Quebec was 379 in 2024, according to the SAAQ census.

How is air pollution from firewood dangerous?

Smoke from burning wood consists of:

  • A complex mixture of gases such as nitrogen compounds (NO, NO2) and ozone (O3), which promotes chronic inflammation, first in the lungs and then throughout the body, thus contributing to cardiovascular disease, and carbon dioxide (CO2), which directly competes with oxygen transport in the blood, further reducing the oxygen supply to our organs;
  • Toxic air pollutants such as dioxins, furans, volatile organic compounds (VOCs, such as benzene and formaldehyde), and polycyclic aromatic hydrocarbons (PAHs), known for their irritant and inflammatory properties, and in some cases, with strong or proven carcinogenic properties;
  • Finally, fine particulate matter.

While gases and toxins are undeniably a problem indoors, these microscopic fine particles (PM) pose the primary issue. Unlike gases, PM accumulates through the eyes and respiratory system, causing various health problems that can become chronic, such as lung diseases like asthma and chronic obstructive pulmonary disease (COPD), and heart disease, as recently highlighted by experts. Using unsuitable appliances, damp or treated wood, or poorly maintened fireplaces and wood stoves will have detrimental effects, particularly for those with fragile health in the short term, and for everyone in the long term.

What are fine particles?

Fine particles less than 2.5 microns in diameter (PM2.5, about 1/30th the diameter of a human hair), such as those found in vehicle exhaust and from the combustion of fossil fuels and firewood, play a major role. A recent study (Fig. 2), based on a retrospective analysis of participants from the UK Biobank in Great Britain, showed a direct association between an increased risk of developing premature cardiovascular disease and rising concentrations of microparticles in the air. This would account for 5% of deaths due to myocardial infarction. This study confirms a previous analysis conducted in Canada that reported a proportional link between hospitalizations for myocardial infarction and environmental concentrations of microparticles from firewood combustion, with a peak in risk during winter when firewood burning is more frequent. It also has the merit of demonstrating that the effects of gases and volatile compounds contained in firewood smoke increase the harmful effects of fine particles. This is important because, while gases can be ventilated and eliminated by our bodies, this is not the case for microparticles, which, once inhaled, accumulate throughout our lives with each exposure.

Figure 2. Impact of increasing air concentration of microparticles on premature development of cardiovascular diseases. HR: hazard ratio; CVD: cardiovascular diseases. Adapted from Luo et al. (2025).

Pollution from microparticles can also have acute effects: in a German study, contact with microparticles of approximately 100 nm was associated with hypertensive crises beginning two days after exposure in at-risk individuals. Asthma attacks receive the most media attention, their increase being linked to urban pollution peaks (i.e., smog), but this German study reveals the insidious effect of microparticles on a condition like hypertension, which often goes unnoticed (i.e., no symptoms felt by the patient) but can lead to a stroke, or, when it becomes chronic, to coronary artery disease, myocardial infarction, and heart failure.
 
The main diseases resulting from PM2.5 pollution are cancers, lung diseases, and cardiovascular diseases. In a review by vascular disease experts, it was reported that acute exposure to PM2.5 induces a loss of the relaxing function of the vascular endothelium, the monolayer of cells that interfaces with the blood and has anticoagulant, anti-adhesive properties for platelets and immune cells, and vasodilatory properties. These functions are among the first to be affected in healthy individuals around the age of 50, and this loss occurs prematurely in the presence of cardiovascular disease risk factors such as ambient pollution from wood fires. The mechanisms of action of PM2.5, which are detrimental to cardiovascular health, are similar to those of the nano- and microplastic particles we recently reviewed.. The entry of microparticles into the lungs causes local inflammation in the bronchi, which can trigger an asthma attack in at-risk individuals. Once in the bloodstream, these microparticles produce systemic inflammation, which is accompanied by increased blood clotting by activating platelets. This can lead to thrombosis and endothelial damage. Repeated exposures result in accumulated damage and an increased risk of myocardial infarction and stroke. These nano- and microparticles from wood burning in the home add to the usual risk factors for cardiovascular disease and work synergistically to accelerate cardiovascular damage.
What concentrations are we talking about?
 
The WHO limits are <10 µg/m³ annually in the atmosphere and <20 µg/m³ daily. In Canada, the annual atmospheric limit is approximately fixed at 12 µg/m³. There is little data on indoor concentrations in Canadian homes: a 2010 Health Canada study reported values ​​below 15 µg/m³ in non-smoking residences and 35 µg/m³ in residences with smokers, which are considered high. In general, PM2.5 levels were lower indoors than outdoors, except in the homes of smokers.
 
In a UK study, detectors were installed both outside and inside 20 homes using wood-burning stoves placed directly in the living areas. First, the study showed that  average daily concentrations of fine particulate matter indoors when a wood stove was in use were 196% higher for PM2.5 (27 compared to 12 µg/m³) and 228% higher for PM1 (particles 1 µm and smaller) (19 compared to 8 µg/m³) compared to the control group not using a wood stove. Second, average hourly peak concentrations were 124% higher for PM2.5 and 133% higher for PM1 than the daily averages, showing that PM saturates indoor spaces. Third, the resulting peaks were directly related to the number of pieces of fuel used and the duration of combustion, suggesting that opening the stove door is the primary mechanism for introducing PM into the home. Finally, the data demonstrate that the observed indoor air pollution was not of outdoor origin.
 
A controlled French study revealed that PM2.5 concentrations during the three-month winter period (January to March) were 5.7 µg/m³ in homes using wood-burning stoves (i.e., a boiler in a dedicated, insulated room, usually in the basement), and that these concentrations decreased by 21% (4.5 µg/m³; p<0.05) in the group of users who had been actively educated about the harmful health effects of wood burning. However, the evidence strongly suggests that the WHO’s threshold values ​​should be lowered, since at a concentration of 5.7 µg/m³, wood burning is already a risk factor for cardiovascular health.
 
Are we aware of the health risks associated with smoke from wood fires?
 
In a recent US study, a sample of the population was surveyed with the following question: Are you concerned about air quality when you heat with wood? As the results show (Fig. 3), very few people are aware of the harmful effects of smoke. This study confirms the French study that demonstrated that raising awareness significantly reduces the use of wood for heating, and therefore, also reduces indoor pollution.
Figure 3. Perceptions about wood heating impacts on air quality in homes and in communities. Adapted from Kilkenny et al. (2024).

What are the regulations in Quebec? The Regulation respecting wood-burning heating appliances, which came into force on September 1, 2009, and was amended on August 27, 2014, and July 8, 2019, aims to prohibit the manufacture, sale, and distribution in Quebec of wood-burning heating appliances that do not comply with the environmental standards of the Canadian Standards Association or the United States Environmental Protection Agency (US-EPA). Certified appliances emit up to ten times less fine particulate matter and three times fewer other contaminants than conventional heating appliances, which are responsible for more than 40% of the fine particulate matter emitted into the atmosphere in Quebec.

What are the levels of fine particulate matter produced by different heating systems? Are certification standards the answer to the problem?

Here are the emissions of pollutants and fine particulate matter from heating systems (Fig. 4).

Figure 4. Diagram of pollutant emissions from different individual heating systems. Adapted from Puget Sound Clean Air Agency, Washington, USA.
 

As Figure 4 clearly illustrates, even EPA-certified wood-burning fireplaces are highly polluting and pose a health risk. It’s important to note that the certification protocols for a stove or fireplace don’t reflect normal use, as these certifications are based on using barkless, very dry, and precisely calibrated wood. However, many variables influence smoke and pollutant emissions, including the quality of the wood (i.e., whether itis green and damp), the intensity of the fire, how the wood is stacked, whether more is added during the burn, the outside temperature, and atmospheric pressure—in short, many variables that are beyond our control in real-world situations.

What are the economic costs of pollution related to wood fires?

In their report, Health Canada experts estimated that the total economic cost of all the health impacts of air pollution in Canada in 2015 amounted to $120 billion, or about 6% of the country’s real gross domestic product. The proportion of PM2.5 produced by residential wood burning is 10% of total production. That same year, the socioeconomic cost of burning firewood reached $11 billion in Quebec alone, more than for all other modelled sectors combined, including road vehicles ($3.1 billion). This does not take into account the increase in forest fires linked to climate change.

In conclusion, these figures are not surprising, since the impact of air pollution on health has been known for a long time. What is most surprising is the scale of the overall impact of wood heating in Quebec, which only concerns a minority of households (between 10 and 15%), as well as the general public’s lack of awareness regarding the impact of this pollution. Without banning wood heating, raising standards to capture as many microparticle emissions as possible would benefit everyone.

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