After years of steep decline, wood heat is back, with people flocking to dealers to buy new wood stoves, wood boilers and stoves that burn pellets made of wood byproducts. Others, to the dismay of environmentalists, are dusting off old wood-burning devices that are less efficient and more polluting.

Air pollution is still a major concern, particularly with wood boilers. A 2006 report found that average particulate emissions from one outdoor wood boiler equaled that of 22 wood stoves, 205 oil furnaces or as many as 8,000 natural gas furnaces.

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