Wood furnaces burn wooden material, such as logs and sticks, to provide heat. The three most common wood furnace types are circulating, radiant and combustion. Circulating wood stoves do not require much space because the unit's outer shell manages to remain relatively cool while in operation. Radiant and combustion furnaces are usually made of sheet metal and iron, causing their outer surfaces to become very hot. Place furniture and other items at least 3 feet away from these types of furnaces. Also, if the furnaces connect to your home's chimney, make sure the connecting pipe is no longer than 8 to 10 feet.
Among the most inexpensive forms of furnaces, in terms of maintenance, are those that run on natural gas. The low cost results from needing only one supply line to operate the furnace. Also, this type of furnace creates little residue or waste. For best effectiveness, place natural gas furnaces at the center of your home. At least 2 feet of space is required in front of a natural gas furnace for air openings into the unit's combustion chamber.
According to the "Poultry Engineering, Economics and Management Newsletter," oil-burning furnaces are more cost-efficient than other types of furnaces because they produce more British thermal units, BTUs, of heat per gallon. Like a natural-gas unit, an oil-burning furnace heats air and releases it into the house. The Chimney Safety Institute of America says oil-burning furnaces emit small amounts of carbon monoxide and that about 200 people die annually of poisoning from their vent systems. In confined spaces, Beckett Residential Burners recommends that you give an oil furnace's openings at least 1 square inch of free space for every 1,000 BTUs per hour that the furnace produces.
A corn furnace burns corn to generate heat. This type of furnace is common in regions with an abundance of corn fields, such as the U.S. Midwest and Southeast. When installing a corn furnace, place the unit near your house's outside walls for venting purposes. The front of most corn furnaces opens so you can remove and clean the unit's ash pan and fire box. Control boards are usually mounted on the sides of corn furnaces. Set your corn furnace at least 4 feet from a door, window or any other air inlet into the house. If a door is below the furnace, make sure the unit is at least 1 foot above the door, Corn Flame Energy recommends.