For most of us, a fireplace is synonymous with a peaceful evening at home, when we can relax and let our minds wander in front of the dancing flames and enjoy the crackling sound of burning logs.
Is it safe?
Whether it comes from a wood stove, fireplace or campfire, smoke isn’t as harmless as we might believe. Wood heating is in fact a major source of air pollutants like carbon monoxide (CO), volatile organic compounds (VOC), fine particles (PM2.5), nitrogen oxides (NOx) and polycyclic aromatic hydrocarbons (PAH). Smoke from the combustion of wood is present both outdoors and indoors.
In neighbourhoods where wood heating is common, residents are exposed to residential wood heating emissions that can have harmful effects on health.
The situation in Québec
In Québec, residential wood heating is the main source of fine particles generated by human activity. The contribution to pollution of this type of combustion varies by locality and can be significant in some. For example, a Communauté urbaine de Montréal (CUM) sampling campaign on wood heating throughout île de Montréal demonstrated that concentrations of VOC, fine particles and PAH in residential areas in winter were often higher than concentrations measured in downtown Montréal.
According to Natural Resources Canada data, the number of households using wood for heating practically doubled from 1990 to 2010. The popularity of wood-burning appliances for heating purposes has increased especially since the 1998 ice storm. The Regulation respecting wood-burning appliances, which came into force in 2009, prohibits the manufacture, sale and distribution of wood-burning appliances that do not comply with environmental standards set by the Canadian Standards Association or the United States Environmental Protection Agency. That same year, the Ville de Montréal adopted a By-Law that prohibits the installation of certain types of combustion appliances on its territory.
The effects of smoke on health
Potential effects on health of high concentrations in ambient air of pollutants associated with wood smoke
Effects may be felt to varying intensity, based on individual sensitivity. Children, seniors and people who suffer from asthma, emphysema or heart problems are the most sensitive to air pollution. Such effects can be exacerbated in winter due to poor air pollutant dispersion conditions, which are more frequent during this season. Poor dispersion conditions trap PM2.5 and other pollutants at ground level, which increases exposure, both for vulnerable individuals and the general population.
Particulate pollution has visible consequences
Among all particles emitted by wood heating, the ones whose aerodynamic diameter is equal to or less than 2.5 micrometres (PM2.5) are of most concern for health. These suspended particles are so small that when inhaled, they cover the surface of the pulmonary alveoli and impair gas exchange, which impacts the respiratory and cardiovascular system by, for example, aggravating symptoms of asthma through the irritation and inflammation of the bronchi. Winter smog, of which residential wood heating is a contributing factor, is mainly comprised of fine particles.
Fine particles and several other air pollutants are measured at air quality monitoring stations throughout Québec. Some of these stations are conveniently located in residential areas where a large proportion of homes use wood heating, thus enabling efficient measurement of its effects on air quality. In winter, the concentration of particulate matter pollution observed at these stations fluctuates with the time of day, with two maximum values. The first is a lower intensity morning peak, attributable to households adding wood to the fireplace before leaving for work. The second, higher value can be observed in the evening, when many residents return from work, restart their wood stoves and keep them burning. This maximum value lasts longer, because winds tend to die down in the evening, and this reduces air dispersion, concentrating pollutants at ground level.
In addition to households that use wood for their heating needs, others may enjoy the pleasant ambiance created by fireplaces. The effect fireplaces have on air quality is particularly noticeable on winter weekend evenings, when particulate concentration rises quickly and can easily double within only a few hours.
Temperature inversions are weather phenomena that impair the dispersion of air pollutants. Under normal conditions, warm, less dense air rises into the upper atmosphere, carrying pollutants with it. This is known as vertical dispersion. Temperature inversions produce the exact opposite by allowing a layer of warm air to remain stationary above a colder air mass, thereby trapping the cold air at ground level. The denser and heavier cold air does not rise under temperature inversion, and prevents vertical dispersion, thus imprisoning pollutants at ground level.
When this natural phenomenon occurs in valleys, the effect is amplified by the topography, since it also prevents horizontal dispersion of pollutants.
In addition to pollutants that are being emitted into the environment, wood-burning appliances may also affect air quality inside the home through combustion gases and fine particle leakage. This can be more or less of a problem, depending on the type of appliance, quality of installation and operational efficiency. A study conducted by the Direction de santé publique de Montréal-Centre (Executive Summary available in English) found that wood-burning appliance users had higher concentrations of pollutants in their urine. Wood heating is therefore an additional source of exposure to toxic substances inside the home.
What should I do?
Here are a few easy things you can do to limit your exposure to pollutants.
If you choose a wood stove
Purchase a certified unit that complies with the Regulation respecting wood-burning appliances and whose specifications sheet shows the lowest rate of particulate emissions.
New fireplaces and stoves that are EPA-certified (Standards of performance for New Residential Wood Heaters),40 CFR 60, subpart AAA or CAN/CSA – B415.1) emit up to 90% less pollution, burn one-third less wood and release 80% less smoke.
While current certified wood-burning appliances are much more efficient than older models, wood combustion still produces more air emissions of fine particles than other energy sources such as fuel oil and gas.
Pellet fireplace and stove combustion is cleaner, because the pellets enter the combustion chamber in a controlled manner, as does air used as an oxidizer. This type of controlled combustion generally produces fewer polluting air emissions than earlier heating appliances, which use ordinary wood.
Before you purchase or install a new combustion appliance, check with your municipality, because some cities regulate the installation and/or utilisation of wood-burning appliances.
Follow the Canadian combustion appliance installation code to ensure that your appliance operates properly and safely.
Maintain, repair, or (depending on your needs) replace your wood-burning appliance. As time goes by, both the appliance and chimney will progressively lose their airtightness and allow gases and particulates to escape. In addition to diminishing energy efficiency, this can impair the air quality inside your home. Regular chimney cleaning leads to optimal combustion and minimizes the risk of house fires.Learn more
Information about residential wood heating is available on various Web sites:
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