How Does a Wood-Burning Furnace Work?

Firebox

The firebox, also known as the combustion chamber, is the heart of any wood-burning furnace. Built out of either metal or brick, this is the area where the wood is burned and heat generated. Wood is fed into the firebox through an opening in the wall of the firebox, which may be covered by a hatch or left open to expose the flames. Heat radiates through the walls of the firebox, with thinner walls giving off a more intense heat in a shorter period of time and thicker walls giving off less heat, but over a longer period of time.

Flue

The flue, commonly referred to as a chimney, is the pipe that removes the smoke and hot gases from the firebox and deposits them into the air outside of the building. Some flues go straight up from the firebox and exit the building rapidly. Other flues form complex patterns in the furnace and zigzag their way to the roof. This is because smoke and gases give off heat, and the longer they are exposed to the room, the more heat they will supply, making them an additional heat source and increasing the efficiency of the wood-burning furnace.