A wood boiler burns wood in a sealed firebox surrounded by a water jacket. A circulator is used to deliver the hot water to the house. It was determined years ago that when water was heated by a wood fire, a drastic temperature drop occured and often created an exhaust problem. In other words, the fire cools down and creosote is produced. A build up of creosote inside the chimney can ignite and become a fire hazard.
One of the remedies was to locate the wood boiler outside the building. The outdoor wood boiler is enclosed in a shed with its own chimney, and located a safe distance from the house. Water lines, connecting the house to the shed, are buried below the frost line. The hot water can be used for domestic tap water via an indirect water heater, or for space heating. Space heating is accomplished via baseboard heat, radiant floor heat, or hydro-air heat, depending on the desired application.The exchange of heat, from wood to water, is less efficient than the simpler exchange from wood to air, and the wood boiler tends to make a considerable amount of smoke. An amount that many people, who usually live nearby, have decided is unbearable. A number of states and municipalities have drawn strict enforcement codes regarding the use of outdoor wood boilers, so check with local authorities before you decide to make a purchase.