Better Woodstove Burning Techniques
Smoke from wood burning is a significant source of air pollution and can have serious health consequences. Common health effects from wood smoke include congestion, headaches, and itchy eyes. Wood smoke consists of small airborne particles that can become lodged in our lungs, making breathing difficult and leading to more serious short-term and chronic health problems for certain sensitive populations, especially those with asthma, respiratory or heart conditions, or other illnesses. Children and the elderly are also at risk.
Woodstove operators can control air pollution from wood smoke and improve a stove's performance by learning to use the stove properly and burning correct fuels. Below is a brief description of key phases in the combustion process and operator tips to assist in achieving a cleaner and more efficient burn.
Stages of Burning
- Evaporation: Before wood can burn, excess water must first be evaporated. The energy required for evaporation is wasted energy, as it could have been used to heat your home instead. Use dried or seasoned wood for a more efficient burn.
- Emissions: As heat inside the stove intensifies, waste gases (smoke) are released from the wood. Unburned smoke is emitted into the air as pollution or condensed in the chimney, causing creosote buildup. A good supply of oxygen will help burn up or diminish waste gases; conversely, starving a fire of air results in a cooler fire and more unhealthful emissions.
- Charcoal: When most of the tar and gases have burned, a bed of coal (charcoal) remains; this bed of coals boosts the combustion process when burning larger pieces of wood. Your best bet is to start with a small fire to develop a bed of hot coals. As the coal bed develops and the stove heats up, slowly add larger and larger pieces of wood, stacking them so that air can circulate freely around them. It takes time to build a good coal bed, but the increased amount of heat makes the extra effort worthwhile.
Tips for Better Burning
Minimize woodstove use on high-risk burning days.
The risk of air pollution buildup is highest on days with poor ventilation (stagnant air). Poor ventilation and temperature inversions trap smoke for extended periods of time near the ground, where it hovers around our homes. During this time smoke from residential wood burning can combine with car exhaust, road dust, and industrial emissions to cause air quality to become unhealthy. Smoke from just one poorly burning woodstove can create serious health problems for the family and neighbors. Avoid burning when ventilation is poor. In addition, check DEQ's daily air quality reports to see if burning has been restricted in your area.
Burn only seasoned wood.
Newly cut logs are 50% water. If you burn logs when they are this wet, a high amount of energy is wasted driving off excess moisture, resulting in very poor combustion, increased pollution, and creosote buildup.
The best fuel is seasoned wood, wood that has been split and dried by air for at least 6 months for softwoods or about 1 year for hardwoods. Seasoned wood has a moisture content of about 20% or less. It tends to be dark in color, cracked on the ends, and light in weight, and its bark is easily broken or peeled. If seasoned wood is not available, manufactured logs made of compressed sawdust are another option.
Do not burn garbage in your stove. Plastics, rubber, paint, oil, painted briquettes, charcoal, and glossy and colored paper release toxics when burned and can cause serious health problems for you, your family, and your neighbors.
Prepare seasoned wood:
- Split wood to help it dry. Wood will dry more quickly and burn best if cut to about 3 1/2 to 6 inches in diameter.
- Stack wood loosely in alternating layers (crisscross fashion) at least 1 foot above the ground and away from buildings. A sunny, well-ventilated area is best.
- Cover wood to protect it from the weather. Leave the sides open to breezes.
- Give it time to reach the 20% or less moisture content required for seasoned wood. This process takes about 6 months for softwoods and 1 year for hardwoods. Think ahead and buy next winter's wood well in advance.
Consider wood heating values
|Species||Minimum Outdoor Drying Time||Heating Value
Million Btu/Air-Dried Cord
|Ease of Splitting||Sparks|
|Cedar||6 months||14-20 medium-low||Easy||Many|
|Douglas Fir||6 months||19-21 medium||Easy||Moderate|
|Madrone||6 months||30 high||Difficult||Very few|
|Maple||6 months||19-21 high-medium||Moderate||Few|
|Oak||6 months||29-31 high||Moderate||Few|
|Pine||6 months||17 medium-low||Easy||Moderate|
|White Fir||6 months||17 medium-low||Easy||Moderate|
Inspect and maintain your stove.
Periodic inspection of your stove or fireplace is essential for continued safe and clean burning:
- Clean chimneys every year to remove creosote buildup and identify potential problems. Ensure the chimney cap is free of debris, and stovepipe angles and bolts are not corroded.
- Replace the catalytic combustor and baffles every 1 to 4 years depending on use, as they are exposed to very high heat and deteriorate with time.
- Replace gaskets on airtight stove doors every few years. Gaskets and seals control the location and flow of air into the appliance.
- Check seams on stoves sealed with furnace cement. Seams may leak and result in heat loss and reduced efficiency.
- Replace broken or missing firebrick.
- Keep the floor of your stove clean of debris and ash.
Burn smaller, hotter fires.
Build small, hot fires instead of large, smoldering ones to reduce smoke and emission of smoke-related pollutants. (Hot temperatures burn off waste gases better than cooler fires.) When starting a fire, keep the damper and other air inlets open for 20 to 30 minutes to allow in enough air to fuel a hot fire. Establish a bed of coals before putting large logs into the stove.
Don't bed it down for the night.
Holding a fire overnight is a fire hazard, and because it does not allow an adequate amount of air into the firebox, creates a lot of smoke and creosote. You will pollute the neighborhood, and the smoke can back draft into the house, causing a serious indoor air pollution problem. Let your fire burn out completely and rely on your home's insulation to hold in enough heat for the night.
Watch your smoke signals!
If you're sending up a lot of smoke, chances are you're burning incorrectly. Apart from the half-hour after lighting and refueling, a properly burning fire should give off only a thin wisp of white steam. If you see smoke, adjust your dampers or air inlets to let in more air. Remember: the darker the smoke, the more pollutants it contains and the more fuel is being wasted.