An add-on wood-burning furnace is a heating instrument that is used in conjunction with a central electric, gas or oil furnace to provide extra heating throughout the home. This supplementary heat source is sometimes called a sidekick furnace or helper furnace and uses wood as its primary fuel.
The add-on wood-burning furnace usually sits in the basement adjacent to the main furnace. Its heat flows through the heating ducts and is pulled through the return air. It is then distributed throughout the home's ventilation system. Add-on furnaces come with their own thermostat and are available with or without an air circulating blower. Those without an air blower use the blower from the primary furnace to circulate heat.
Some add-on furnace models can burn coal, shelled corn or biomass fuels in addition to wood. This ability to utilize renewable fuels provides potential cost savings and environmental benefits. Add-on furnaces can also be used as wood-burning stoves. The furnace's back and sides must be at least 18 inches away from any combustible surface, and it must have 4 feet of wood- loading clearance in front of it. Add-on wood burning stoves are subject to local code requirements for combustible surface clearance and chimneys.