Wood and Appropriate Wood Products

• Wood furnaces are, of course, designed to burn primarily wood and wood products. While almost any wood will burn in a wood furnace, experts at Hearth.com recommend burning seasoned wood because it burns hotter, more efficiently and contains less moisture than other wood products. Green and unseasoned wood products generally contain high amounts of water, and this moisture sometimes comprises up to half of the wood's weight; for this reason, green wood typically burns inefficiently, as the moisture must be extracted and eliminated by the furnace before the wood can produce useful heat. Wood products, like discarded furniture and wooden pallets, are usually also safe to burn in wood furnaces, though furnace-repair experts at Service Magic recommend avoiding driftwood, treated or painted wood products, or any wood items that contain sulfur or lead, as the resulting fumes from these products can adhere to the inside of a wood furnace and inhibit its operation.
  
  

Coal

• Many wood furnaces are designed to burn coal. Formed from plant and animal remains buried for millions of years, coal packs a high energy output into a relatively small package. Coal should only be burned in wood furnaces that were designed for coal use and carry an "Approved for coal fuel" placard or sticker. Coal does not burn as cleanly or efficiently as wood, and wood furnaces that are not designed to be compatible with coal fuels may quickly gum up and break as coal residue collects inside the combustion chamber and ventilation system.
  
  

Materials to Avoid

• Although some wood furnaces are designed to work with coal, and a select few may also burn oil, wood furnace owners should never attempt to fuel their furnaces with alternate fuel sources, regardless of how available or convenient the materials may be. According to experts at Hearth.com, trash placed into a wood furnace can quickly escalate into a chimney fire, and some plastics and treated products commonly found in refuse contain toxic chemicals that are released in high-heat environments. Unapproved products can also damage sensitive components of the wood furnace, leading to expensive repairs that may not be covered under the furnace's warranty.