Wood Stove Emissions - Background

With the increasing use of wood stoves nationwide, there is growing concern about the health and environmental effects of wood smoke. The burning of wood is known to produce a complex mixture of particulate and gaseous emissions. It can be a local problem because wood smoke is typically emitted close to the ground and is highly dependent on wind characteristics to dilute or disperse it.

What pollutants are emitted in wood smoke?

Wood smoke contains large amounts of particulates, carbon monoxide and organic compounds. Other significant combustion products include nitrogen oxide, benzo(a)pyrene, napthalene, arthracene, phenanthrene, biphenyl, fluoranthene, pyrene, chrysene, benzene, pyrelene, dioxin and heavy metals.

What are the health effects of these pollutants?

Many of the particulates contained in wood smoke are small enough to penetrate deeply into the lungs, and from there into the bloodstream. The particles typically are composed of a carbon core with irritants and toxic compounds on their surfaces. Once these particles have penetrated the body, they can have a wide variety of adverse effects, such as difficulty breathing, respiratory and heart disease, or cancer. The impact on individuals will vary with the amount of smoke that they breathe, their stage of development, and any pre-existing health conditions. People with asthma, chronic lung disease, heart disease, as well as growing children and women who are or may become pregnant are more susceptible to impacts from wood smoke.

Is wood smoke a problem in Maine?

Yes and no. Ambient air monitoring conducted in Maine has not specifically identified wood smoke as a principal contributor to violations of air quality standards. However, ambient levels may be creating an unacceptable cancer risk, and DEP monitoring studies do indicate that some neighborhoods can experience greatly elevated pollutant levels caused by wood stove emissions. In such areas, there should be some concern, and residents should work to improve burning practices and reduce emissions. People who have wood stoves in their home need to be especially diligent about preventing smoke from blowing back into the house.

What action has EPA taken regarding wood stoves?

The U.S. Environmental Protection Agency was concerned about wood smoke impacts and therefore developed regulations to reduce wood stove emissions. EPA established emission limits that all wood stove manufacturers must meet.

All wood stoves manufactured after July 1, l988, were required to meet "Phase I" emission limits. On July 1, 1990 more stringent "Phase II" limits took effect. These standards require that new stoves with catalytic converters must be designed to emit less than 4.1 grams of particulate matter per hour; stoves without catalytic converters must be designed to emit no more than 7.5 grams per hour.

EPA also conducts a certification program for wood stoves. All manufacturers are required to test their stoves and report the results to EPA. If you're buying a wood stove, look for a temporary label providing information on pollution levels, efficiency, and heat output as well as a permanent label documenting that it meets EPA emission standards.

In more recent years, stove manufacturers have devised a new technique for reducing air emissions by increasing the air flow volume passing through the stove, thereby increasing the burn rate. If the stove you're interested in does not have an emissions testing certification label, inquire whether it is one of those newer stoves that have such a high excess air flow that it does not fall under the requirements of the EPA wood stove certification program. With the stove identification and air flow information, you can then ask the DEP or EPA staff to verify that for you before you make a purchase.

Can regulations totally solve the wood smoke problem?

No. Stoves must also be properly operated to take advantage of the stove's pollution control equipment. Even if you don't have a catalytic converter-equipped or high-efficiency stove, following these guidelines will improve the stove's performance and reduce pollutant emissions:

* Weatherize your home. Insulation, storm windows, weather stripping and caulking all reduce energy needs and decrease the amount of wood required to heat a house.

* Size your stove properly. A stove that is too large for the space to be heated will have to be damped down too low. A slow burning, smoldering fire causes much more air pollution than a hot burning fire.

* Burn seasoned wood. This will increase the efficiency of the combustion process and will help you get more heat and less smoke. (Green wood contains up to 50% water.) If possible, have your firewood delivered in the spring of the year so that the green wood can dry out or "season" before the fall and winter heating season. Better yet, have it delivered one year ahead of when you need it.

* Burn small, hot fires. These decrease the amount of creosote produced and create less pollution. Even though small, hot fires require more frequent loading and tending of the stove, and the improved efficiency and decreased air pollution are worth the effort. When you load your stove, be sure the flue dampers are open so that smoke doesn't get back into your house. Open the firebox door slowly to allow the fire to adjust to the increased air flow.

* Install a stove pipe thermometer. Frequent observation of pipe temperatures and adjustment of air flow to the fire will promote better combustion and result in fewer emissions. The most efficient and least polluting temperature range for a wood stove results in stove pipe temperatures of 300 to 400 degrees Fahrenheit.

* Remove excess ashes. Ashes can clog a stove's air intake vents and decrease the amount of oxygen and turbulence required for cleaner more efficient wood burning.

* Clean the stove pipe and chimney. Cleaning the stove pipe and chimney promotes a good, consistent draft for your stove and reduces the risk of a chimney fire. Do this a minimum of once a year or whenever the creosote builds up to 1/4 inch in thickness.

* NEVER burn pressure treated wood, creosote treated timbers, plastic or garbage in your wood stove or outdoors. Burning these materials is prohibited because, when burned, these materials release toxic compounds and heavy metals that can threaten your health and the health of those downwind of you. Although not prohibited, burning painted wood can also emit such pollutants to the air.

How can I get additional information on wood stove emissions:

For more information, phone DEP's Bureau of Air Quality Control in Augusta at 287-2437 or toll free at 1-800-452-1942, or email us with your questions.