How Wood Furnaces Work


Indoor and Outdoor Furnaces

  • Wood furnaces are available in both indoor and outdoor varieties. Though there are some basic differences between the two types of wood furnaces, although the overall functionality remains the same for both types. Indoor wood furnaces are generally smaller and are designed to vent all of their smoke and other exhaust outside through a chimney unit, while outdoor wood furnaces tend to be larger and are able to vent with a shorter smoke stack. Both furnace types use wood or other biomass material to fuel a fire that in turn heats water contained within the furnace unit. The heated water is circulated into a radiator that is attached to the ductwork of your house; a blower or fan then helps the heat to transfer into the air and circulate throughout the heating ducts. Cool water returns to the main furnace unit to be heated again.

Wood Furnace Construction

  • Regardless of whether a wood furnace is an indoor or outdoor model, some design elements remain the same. The furnace will feature a sealed firebox to contain the wood or biomass fuel that is being burned, as well as some form of ventilation holes to allow air to enter the firebox without creating a hazard. The firebox is contained within the main furnace cabinet, which has fully closing doors on it that can be opened if the fire needs to be stoked or additional fuel needs to be added. The firebox connects to the circulation pipes for the water system that transfers heat from the furnace to your home heating ductwork, which in turn connects to the blower that aids in the movement of heated air throughout the house. The furnace will also feature a chimney or smoke stack so that smoke and other gasses can be vented into the open air outside of the house.


  • Because wood and other biomass fuel produces ashes and soot, regular cleaning of a wood furnace is important to keep it in proper working order and to prevent the risk of fire or other malfunctions. The ventilation holes that allow air into the firebox should be cleaned so that the fire can get enough air to burn, and the chimney or smoke stack should also be cleaned so as to prevent buildup that can lead to a backup of smoke or other hazardous gasses. Should the furnace feature a thermometer that allows you to monitor the temperature of the fire inside the firebox, this thermometer should be checked periodically to make sure that it is still functioning properly.

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