Earthtalk :: Outdoor Wood Boiler Woes

getty images

From the Editors of E/The Environmental Magazine
Dear EarthTalk: Several of my neighbors have installed outdoor wood furnace boilers to heat their homes instead of relying on oil or natural gas. But is all the smoke these boilers create good for my health? -- Susan MiHalo, Michigan City, IN

As the price of fuel has risen in recent years, more and more homeowners across North America are turning to alternative ways of heating their homes. While some might opt for forward-thinking alternatives--like tapping solar, wind or geothermal sources of energy--others prefer to step back to perhaps the oldest source of heat, burning wood. For those with easy access to firewood and the need to heat a large house or multiple buildings, outdoor wood furnace boilers are an obvious, though potentially noxious, choice.Outdoor wood furnace boilers, also known as outdoor water stoves and outdoor wood furnaces, usually consist of a wood-burning firebox surrounded by a water reservoir or "jacket." Ideally a tall chimney vents the unit of the sometimes-copious amounts of wood smoke generated. The combustion of wood in the firebox heats the water in the surrounding jacket, which is in turn pumped via insulated underground pipes into one or more nearby buildings.

Once inside a building, the heated water warms the home via radiators or a heat exchanger duct system. Outdoor wood furnace boilers also typically provide hot water for the home. And, unlike with indoor wood burning stoves, no smoke gets into the house.

While this may all seem well and good, such boilers often become bones of contention between neighbors, as the wood smoke produced can cause hazy banks of smog over entire neighborhoods. According to environmental toxicologist Uni Blake, wood smoke is a complex mixture of chemicals and particulates. It contains carbon monoxide and other organic gases, particulate matter, chemicals, and some inorganic gases. Some of these compounds, such as aldehydes and phenols, are toxic, while others, like benzoprene and cresols, are known carcinogens, Blake reports.

The U.S. and Canadian governments have yet to issue any regulations regarding the manufacture or usage of outdoor wood furnace boilers, so perturbed neighbors don't have much of a legal leg to stand on. But several American states and a few Canadian provinces have called on their capitals to regulate the emissions of these boilers, so time will tell whether or not any formal rules are put into place.

Forward-thinking manufacturers are not waiting to find out, however, and have been busy retooling their units to help maintain optimal combustion conditions and better disperse waste smoke. Meanwhile, owners of outdoor wood furnace boilers can use their units more responsibly by limiting operation to wintertime when neighbors are more likely to be indoors with their windows shut, choosing and burning dried wood so as to minimize the moisture that leads to the creation of smoke, and installing taller chimneys to help disperse the smoke away from nearby homes.

CONTACTS: Washington State Department of Ecology's Fact Sheet on Outdoor Wood-Fired Boilers.

GOT AN ENVIRONMENTAL QUESTION? Send it to: EarthTalk, c/o E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881; submit it online, or e-mail: Read past columns at: