Indoor wood boilers sold in the U.S. after 1992 are safe, as they have clean burning certification and the Environmental Protection Agency has tested them to its standards, states the EPA. The EPA advises all owners to replace old boilers with EPA-certified ones.
Smoke from wood that is not burning properly causes wood smoke pollution. The smoke contains hazardous air pollutants, fine particle pollution (ash), and volatile organic compounds. Health hazards from inhaling such smoke include serious respiratory problems such as asthma and lung cancer.
Burning clean hardwood or wood pellets, using small pieces of wood and not overloading boilers also ensure safer burning.