HEC has, in recent years, focused on toxic threats from Outdoor Wood Boiler (OWB) smoke. An OWB is a technology that looks, from the outside, like a small metal shed with a smokestack 8 to 10 feet above ground level. Inside, wood is burned to boil water that supplies heat through water pipes. Typically an OWB would be located some distance from a house and run water pipes to transfer heat for both space and water heating.

The EPA estimates that most OWBs have only a 30 to 50 percent combustion efficiency. OWBs can be especially a problem if an OWB has a small smokestack height and/or a short distance from a neighboring property.

OWBs’ basic design causes fuel to burn incompletely, or smolder, resulting in thick smoke and potentially high air pollution emissions. Due to OWBs’ shorter smokestacks, smoke and fumes are often poorly dispersed, resulting in a high concentration of thick black smoke that can be hazardous to neighbors. Wood smoke contains a number of organic compounds that are known carcinogens, and high exposure may raise the risk of chronic lung disease and lung cancer. Wood smoke also interferes with normal lung development in infants and children, and increases the risk of asthma and respiratory infections such as bronchitis and pneumonia.

Operating year round, a single OWB can emit 1.55 tons of matter such as dust and soot, which is around the same amount as 50 diesel trucks. Even more alarming, OWBs are only supposed to be powered by dry wood, but some users burn treated lumber, painted wood, cardboard, and trash, which can be especially dangerous to the health of neighbors.