In recent years, Environment Canada has issued increasing numbers of winter smog alerts. Among the main culprits: wood-fired heating systems. It is estimated that close to 100,000 homes on the Island of Montreal alone are heated this way. Across the province, one home in five homes uses a wood-burning system. In 70% of cases, wood is used as a secondary source of heat (e.g., wood stove or fireplace).
Facts about heating with wood
A wood fire has traditionally been prized for its ambience and comfort. We now know, however, that fireplaces and stoves pose significant pollution and health risks: the smoke produced by the wood as it combusts contains about 100 different toxic substances spewed forth in the form of fine particles — including several known carcinogens. More than 95% of these are fine particles, so tiny that they penetrate deep into lung tissue. Very young children, elderly people and sufferers of asthma, emphysema or cardiac problems are particularly sensitive to fine-particle emissions. According to Norman King, epidemiologist with the Montreal Public Health Department, they can lead to irritation of the eyes and respiratory passages and worsen the condition of people living with chronic heart and respiratory diseases.1
In winter, nonexistent or very weak winds combine with temperature inversions to trap pollutants emitted from chimneys close to ground level, forming a yellowish cloud known as smog. It is often accompanied by the odour of smoke. The same toxic smoke can spread insidiously inside your home if you heat with wood. Smoke spillage, as it is called, can be caused by outside chimneys connected to long flue pipe assemblies with multiple 90° bends, negative air pressure inside the house, or a smouldering fire. As one publication puts it: “The smell of wood smoke inside your home is a sign that the wood-burning system isn’t working properly.”2
If you have a wood-burning system, you should obviously stop using it whenever a smog alert is issued by public authorities. More generally, it is also advisable to upgrade to more modern (i.e., low-pollution) equipment.
Secondary heating sources (e.g., stoves and fireplaces) that are certified low-emission by the U.S. Environmental Protection Agency (EPA) can reduce fine-particle emissions by up to 80%. These so-called advanced-combustion or high-efficiency systems feature innovations such as insulated fireboxes that keep temperatures high, and secondary combustion zones where gases are burned completely. These appliances generate more heat and less smoke, burn about 33% less wood than a conventional fireplace or stove, and reduce creosote buildup in chimneys.
CSA International, formerly the Canadian Standards Association, also issues certification for wood-burning stoves and fireplaces. The standard is CAN/CSA B415.1; look for it on appliances as proof of energy efficiency.
There are also more eco-friendly fuel options on the market that provide an alternative to natural wood and can be burned in the same appliances.
Densified wood logs (made from compressed wood residue) have been shown to produce between 30% and 50% fewer fine-particle emissions than natural logs, while offering an energy efficiency improvement of 20% to 35%. This superior performance results from their low moisture content — about one-quarter that of conventional firewood — which in turn causes them to burn at much hotter temperatures.
Paraffin-coated logs, meanwhile, generate up to twice as much heat as wood logs when burned. That heat intensity, however, requires that they be used only in an open stove or fireplace — which means they are less energy-efficient. The same is true of logs processed from coffee grounds, available from some supermarkets.
Sensible heating practices
Obviously, intelligent heating practices go a long way toward ensuring lower smoke emissions from wood-burning systems, both inside and outside your home. You should always use clean, dry wood, build smaller fires with abundant flames, and make sure sufficient air reaches the burning logs and improves combustion.
Remember that in an efficient system, the smoke itself will burn, because the temperature is high enough and sufficient oxygen is present. If not, a great deal of the wood’s total energy will literally go up in smoke, via the chimney.
Finally, a reminder: never burn household garbage (including plastic and cardboard) or green, painted or stained wood in a heating appliance.
Other ways to help reduce smog:
- If you own a oil- or gas-fired heating system, ensure its periodic
- Use a burner with a high energy-efficiency rating.
- Use public transit.
- In cold weather, warm up your vehicle’s engine for no more than
- Don’t let your vehicle engine idle needlessly.
- If you own more than one vehicle, use the one with the best fuel economy
as often as feasible.
- Plan your trips so as to avoid rush hours and/or combine several trips
- Ride a bicycle, weather permitting.
1 Wood Heating: A Burning Health Issue, available on the websites of Environment Canada, the Montreal Public Health Department and the City of Montreal.
2 A Guide to Residential Wood Heating, published by Natural Resources Canada.