Environmental Quality Branch

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Reducing Wood Stove Smoke: A Burning Issue

Last Updated: February 2007

Wood Stove Smoke: A Burning Issue

How many times have you gone for a walk on a cold, still night, and caught the scent of wood smoke in the air? Wood smoke curling out of home chimneys looks and smells cozy, even romantic.

Appealing and "natural" as it seems, wood smoke has become the most serious kind of air pollution in B.C. at present, causing more illness and deaths (from lung and heart disease) than smog. That's because wood smoke contains fine particulates, and a bewildering array of organic and inorganic compounds — the normal byproducts of wood combustion. It may also contain minute amounts of dioxins and furans, and a variety of other proven and suspected carcinogens.

The Ministry of Environment is committed to stopping smoke pollution, in order to protect our health, the environment and the economy. Since 1992, B.C. has been leading the way in Canada, taking action to reduce fine particulate emissions from residential and industrial wood burning.

As we'll see below, this includes initiatives to control smoke from land clearing fires, beehive burners, backyard burning and the wood-burning appliances used to heat many of our homes. ("What's the Government Doing to Prevent Wood Smoke Pollution.")

What's in Smoke and How It Can Hurt You

Fine Particulates: Fine particulates are very small, solid or liquid particles, in many shapes and sizes. At their largest, they are 10 micrometres in diameter, about the size of bacteria. They can easily be inhaled deep into our lungs, collecting in the tiny air sacs (called "alveoli") where oxygen enters the blood. As a result, they can cause breathing difficulties and sometimes permanent lung damage. They are also often composed of harmful substances — for example, toxic trace metals like lead and cadmium, PAHs (some PAHs can cause cancer), VOCs, carbon monoxide and formaldehyde.

Exposure to high levels of fine particulates is associated with a significant rise in respiratory and heart illnesses, and premature deaths. The respiratory disease includes asthma, bronchitis, pneumonia and emphysema. Senior citizens, infants and people who are already sick are most at risk, but healthy younger adults and children can also be affected. At current levels, fine particulates are the most serious kind of local air pollution in British Columbia.

Contact us for a complete fact sheet on fine particulates, entitled Fine Particulates: What They Are and How They Affect Us.

Smoke in British Columbia

British Columbia's climate, topography and settlement patterns make it particularly susceptible to air pollution from wood smoke. The valley bottoms where many interior communities are located frequently experience long periods of cold, stable air during the winter. Wood burning tends to reach its peak on these cold, clear, calm nights — the very time when the atmosphere's capacity to disperse emissions is at a minimum. Pollutants from wood smoke can be trapped and concentrated near the ground during these periods, reaching very high concentrations.

To make matters worse, people often try to make their final load of fuel last all night by damping the air supply as much as possible. The result is a smouldering fire and a great deal of smoke with all its pollutants. This harmful smoke tends to linger near its source, rather than dispersing outwards or upwards. It has the greatest impact near or even inside the homes that produce it.

Some smoke particles are so tiny that they can seep into neighbouring houses — even around closed doors and windows. Inefficient wood stove operation and poor stove design have as much to do with this problem as weather and geography.

To reduce wood smoke, we need to pay closer attention to what we burn, and when, where and how we burn it. A few simple steps can make wood stoves much more efficient. Not only will this cut down on harmful emissions; it will save fuel dollars.

How You Can Increase Wood Stove Efficiency
... and Decrease Smoke

Think of greater efficiency in terms of more heat staying indoors and less going up the chimney. Two things affect efficiency: the stove you choose, and the way you use it .To heat efficiently with wood, you must have a stove that is matched to your heating needs. It must be properly installed, operated within its optimum heating range, and regularly maintained. It cannot be truly efficient unless your home is also properly insulated and weatherproofed.

How to Choose a Wood Stove

Design and Installation
Smoke is generated by incomplete combustion, which can be caused by lack of oxygen, low burning temperature, wet or green wood, and other factors. Generally, any stove design feature that's been proven to promote more complete combustion is desirable. These features include insulated baffles heated primary and secondary air, firebox insulation, and advanced designs that promote secondary combustion.

Baffles
If combustion gases go up your chimney without being fully burned, much of the energy in your firewood is wasted. Baffles increase the efficiency of your stove by increasing turbulence. They hold the gases inside the firebox longer, directing them back into the fire so they will burn more fully and make the fire burn hotter. An insulated baffle keeps the temperature of the gases high to promote this secondary burning.

Air Supply
Inside the stove, pipes or channels allow preheating of the primary and secondary air which can mix with the smoke and ignite to give secondary combustion and ensure that combustion is more complete.

Firebox
Firebox insulation (such as firebrick) stores heat and keeps the combustion temperature high and stable. Heat storage warms your home long after the fire is out. A consistently high firebox temperature promotes more complete combustion.

Certification and Emission Standards
The Canadian Standards Association (CSA) has developed an emission standard (CSA B415.1-100) for wood stoves, inserts, cook stoves, small fireplaces, furnaces and boilers. This standard recommends that emission levels of wood stoves manufactured in Canada meet requirements equivalent to the standards of the US Environmental Protection Agency (EPA) (1990). Many of the stoves manufactured in B.C. are also sold in the US, and already meet EPA emission standards.

In the United States, wood stoves have been regulated for some time by the EPA. Stoves must be tested, and their emissions monitored, to determine the level of particulates they produce. Stoves cannot be sold to the public unless their particulate levels meet the EPA emission standard. Certified stoves can reduce smoke emissions by as much as 90% compared to conventional stoves, and are much more efficient. If your stove is more than 14 years old, consider getting one of the new advanced combustion units.

These certified stoves often include design features that promote secondary combustion. Most of these features are aimed at burning off the dangerous chemicals and toxic substances before they leave the firebox. This is achieved when:

• the fire has an adequate oxygen supply;
  
  
• the gases coming off the fire are at high temperature and are mixed with preheated air (oxygen); and
  
  
• the gases have enough time to burn before they cool down.

Wood Stove Technologies
There are many different stove designs, but most fall into 3 basic technologies: advanced combustion, catalytic combustion, and densified pellet combustion.

Advanced Combustion Stoves
Advanced combustion systems create the conditions necessary to burn combustible gases. Their features include:

• Firebox lining that keeps temperatures high;
  
  
• Devices that deflect gases back into the flames so that they burn more completely; and
  
  
• Heated secondary air supplies that ensure that enough oxygen is present and the temperature remains high.

Canadian manufacturers, including B.C. companies, have established an international reputation as designers of some of the most effective advanced combustion appliances in the world.

Catalytic Stoves
A catalyst is a substance that affects a reaction without being consumed in the process. In wood-burning stoves, exhaust gases can be routed through a catalytic combuster: a ceramic honeycomb coated with a metal such as platinum or palladium. Smoke gases and particles pass through the combuster and ignite at a much lower temperature (250°C) than they would without the combuster (500°C). The result is that harmful substances are more completely burned. The fuel produces more heat through an extended clean burn. However, catalysts can deteriorate over time and must be replaced.

Pellet Stoves
Wood pellets are made of wood byproducts that are dried and compressed into cylinders 25 mm long by 6 mm thick (one inch by a quarter-inch). Pellet stoves include a hopper to hold the fuel and a screw auger (usually electric) to move the pellets from the hopper into the combustion chamber. Pellets usually burn cleanly because they're fed to the combustion chamber at a controlled rate and are matched with the right amount of air to maintain an optimum burn rate. That's why they have the potential to operate at significantly lower emission levels than cordwood stoves.

Most pellet stove designs require electricity to operate their fans and auger motors. Therefore, they do not operate during a power failure. They tend to cost more than wood stoves and they need regular service. But they have advantages over cord wood stoves, in addition to significantly lower emission levels: easy loading, convenient, automatic operation, and precise control over heat production.

All wood-burning stoves must be properly installed to be safe and efficient. Follow the manufacturer's instructions on clearances and connections. Make certain the installation conforms with B.C. building codes, local requirements, CSA safety standards, and local fire safety codes. Ensure that the chimney system is the proper size and is approved. Consult your fire department or building inspector before installing any wood heating unit and chimney system.

Operating a Wood Stove

Choosing a Fuel
Air-dried hardwood, seasoned for a year, is the best cord wood fuel. In B.C., though, people burn mainly softwoods. Seasoning the wood for at least six months, and keeping it sheltered from the weather, is strongly advised. Freshly cut wood is between 35 and 50 percent water by weight. If you don't reduce its moisture content to below 25 percent by seasoning it, much of its heating value will be wasted in burning off this excess moisture. Burning wet or green wood means more trips to the wood pile, potential creosote problems in your chimney (a safety hazard), and higher heating costs.

The use of properly sized pieces is equally important. Wood should be split to a maximum thickness of 10-15 cm (4-6 in), depending on stove size. This size increases the surface area exposed to flame, resulting in higher burn efficiency. Keep a good supply of the driest wood for kindling.

Household wastes such as plastic, painted wood, manufactured wood products and wood treated with preservatives release very toxic chemicals when they're burned. Don't burn these materials in residential stoves or fireplaces, or in backyard fires of any kind.

Coal burns efficiently only in specially designed and CSA/ULC approved stoves and inserts, and burning it in a wood stove may produce excessive and highly toxic emissions. Coal also burns hotter than wood, and can cause a fire hazard if you burn it in a wood stove.

The driftwood found on B.C. beaches may seem like an economically attractive heat source. Driftwood, however, is laden with salt, and burning it releases sodium and chlorine ions. The potential exists for these chlorine ions to form chlorinated compounds such as dioxins and furans, which are suspected human carcinogens. They may also corrode your stove and venting system.

Starting the Fire
Many of today's wood-burning appliances require specific lighting techniques. Always follow the manufacturer's recommendations. Here are some general tips for cordwood stoves:

• Put crumpled newspaper in the stove (don't use coloured or gloss paper). Be generous. Put 10 to 15 small pieces of finely split dry kindling on top of it and behind it. Open the air supply vent wide.
  
  
• Light the paper in several places near the air inlet. Leave the stove door unlatched until the fire is going well. It may be necessary to leave it unlatched for up to 15 minutes until the chimney is primed and the combustion chamber and air supply pipe have been warmed up. Do not leave the stove unattended during this time. Burning embers may fall out.
  
  
• When the flames from the kindling just begin to subside, add at least three small pieces of firewood. Be careful not to smother the fire with the new pieces.

• Gradually increase the size of the pieces as the coals build up.
  

Maintaining the Fire
The key to maintaining a good fire is careful control of the air supply, which determines how completely the fuel is burned. When you start a fire or add wood to a fire, the fresh fuel requires much more air for the first 10 to 15 minutes to complete the rapid combustion phase. Once the wood is well charred, it requires much less air. Loosely stacked pieces burn quickly because the combustion air can reach all the pieces at once. Never add just one or two pieces of wood; three or more are needed to form a sheltered pocket of glowing coals that sustain the fire.

Monitoring the Fire's Performance
Watching both the fire and what comes out the chimney is the best way to monitor your wood stove's performance. Look at the fire first. Is it burning brightly? As your wood decomposes, it vaporizes into smoke: a cloud of combustible gases and tar droplets. The smoke will burn over top of the main fire in a yellow/blue turbulent flame that shows the secondary combustion. Secondary combustion produces bright, lively flames. Dull, steady flames, on the other hand, are a sign of oxygen starvation and incomplete combustion.

Excessive smoke from a chimney in the middle of a burn is another sign of incomplete combustion. Smoke is energy going to waste, and creating problems to boot. Some smoke should be visible when you light the fire, but for the remainder of the burn it should be almost invisible. If the smoke doesn't burn in the firebox, it will go up the chimney. Some of it will then condense to form flammable creosote deposits that can lead to a chimney fire, or leave as air pollution.

Overnight Fires
When you use your wood stove as an overnight heat source, it's important to load it properly to avoid a smouldering fire.

To build a long-lasting fire, rake the coals towards the air inlet and use larger pieces of wood placed compactly in the firebox behind the coals. Place the pieces close together to prevent the heat and flame from penetrating the new load, saving the buried pieces for later in the burn. Open the air inlets fully for 15 to 30 minutes, depending on the size of the load and its moisture content. When the outer pieces have acquired a thick layer of charcoal, reduce the air supply in stages to the desired level. The charcoal insulates the rest of the wood and slows down the release of combustible gases. This allows you to turn down the air control and still maintain a clean-burning fire.

What's the Government Doing to Prevent Wood Smoke Pollution?

In 1994, the B.C. Government passed a regulation aimed at keeping smoke from new wood stoves to a minimum. The Solid Fuel Burning Domestic Appliance Regulation specifies particulate emission limits, and labeling and testing requirements for new wood stoves, fireplace inserts and factory built fireplaces manufactured in B.C., or sold or imported for use in B.C.. Beyond this regulation, the government has moved to control other sources of smoke in B.C., and encourage the use of wood and leafy residue as a resource. It has done so by setting regulations, along with taking nonregulatory actions — such as programs, technical support and public education. The B.C. Government has passed the following two regulations, along with the above-mentioned one:

• Open Burning Smoke Control Regulation (April1993, amended in 1998 and 2000)
  The Open Burning Smoke Control Regulation is meant to encourage the reduction and reuse of vegetative debris from large outdoor fires which are usually set for land-clearing, construction or forestry operations.
  
  
• Wood Residue Burner and Incinerator Regulation (December 1995, includes amendments up to 2004)
  Under this regulation, wood residue (beehive and silo) burners in populated areas (Tier 1) are to be shut down by the end of 2007. Of the original 80 Tier 1 burners, 73 have now been shut down. Eliminating these inefficient burners, which frequently cast palls of smoke over many valleys, will lead to cleaner air in many regions.

To make it easier for municipalities to pass their own "anti-smoke" bylaw, the ministry created a model bylaw on backyard burning in December 1997. Municipalities can use this model to draft a specific bylaw to limit or prohibit backyard burning. See the Model Municipal Bylaw for Regulating Backyard Burning (PDF: 131 KB / 18 pages).

With respect to nonregulatory approaches, the Environmental Quality Branch has given educational and technical support to municipalities and the public — on proper burning techniques, wood stoves, backyard burning restrictions or bans, and composting.

Along with smoke, vehicle exhaust is a major source of fine particulates. To reduce fine particulate pollution in the Lower Fraser Valley, the B.C. Government launched the AirCare ON ROAD (ACOR) vehicle emission testing program in 1999. ACOR targets heavy-duty, diesel trucks and buses — key culprits when it comes to fine particulates and other air pollution. Vehicles that fail the emissions test must be repaired and re-inspected before they can qualify for insurance renewal.

B.C.'s tailpipe standards for new vehicles (see the regulations on our Vehicle Emissions website), the AirCare vehicle-emission testing program, and the older-vehicle "Scrap-It" program are all working to stop the production of secondary particulates. Secondary particulates are formed due to a chemical reaction involving gases emitted into the air. In this case, sulphur dioxide, nitrogen oxides and hydrocarbons released by vehicles are transformed into sulphates, nitrates and organic carbon compounds, respectively.

It's Up to Us

"Where there's fire, there's smoke" doesn't have to be true. Each of us can do our part to stop smoke pollution. Choose a clean-burning stove, and burn clean!

For More Information:

Environmental Quality Branch
Ministry of Environment
Government of British Columbia

PO Box 9341
Stn Prov Govt
Victoria, British Columbia
Canada V8W 9M1
http://www.env.gov.bc.ca/air/