Types of Forced Air Furnaces
- Many American homes are heated with forced air furnaces, which operate in the following manner: A fuel source is burned and the heat is transferred to a metal enclosure called a heat exchanger, which is filled with normal household air. When the temperature within the heat exchanger rises, an electric fan called a "blower" forces the warm air through metal ducts into the household living space where it exits through floor- or wall-mounted registers. What separates one forced air furnace type from another is the fuel source.
- Wood is a common fuel source in many forced air furnaces.campfire full of burning wood image by Irina Igumnova from Fotolia.com
Many people, particularly those living in rural areas, heat their homes with furnaces designed to burn wood. If they can cut and harvest their own wood, their fuel is essentially free. Wood-fired forced air furnaces are installed both inside or outside a dwelling. Their primary disadvantage is that they require monitoring to ensure the fire does not go out. - Other homes are heated with oil-fired furnaces. Heating oil is a refined form of kerosene. It is clean burning, and if the burner and furnace are regularly serviced, it produces no telltale kerosene odor. The fuel for an oil-fired forced air furnace is stored in a large tank that is usually gravity-fed through a copper fuel line. To avoid running out of heating oil, many homeowners sign long-term supply contracts with local heating oil distributors.
- Anthracite coal is an excellent fuel source for a forced air furnace.Close-up of coal image by Marek Kosmal from Fotolia.com
Another common type of forced air furnace uses anthracite (hard) coal as the fuel source. Like a wood furnace, it is stoked by hand and monitored to ensure that the fire does not go out. Periodically the homeowner must clean out the ash bin and dispose of the burned cinders. Coal furnaces burn a variety of coal sizes including rice, pea, chestnut or egg. Some coal furnaces contain a shelf inside the firebox where the owner can cook things like baked beans or casseroles. - Flammable gases, such as natural gas or propane, are also used to fuel some types of forced air furnaces. Natural gas enters the house from underground gas lines. Propane is stored outside in large tanks and fed to the furnace through copper gas lines. Propane furnaces are more common in sparsely populated areas where gas lines are not installed.
- Some types of forced air furnaces are designed to accept and burn a wide variety of fuels. Referred to as combination, or multi-fuel furnaces, some burn cord wood, wood pellets, cherry pits, coal or even shelled corn. Like wood furnaces, they are more commonly installed in rural areas with access to one or more of the fuels referenced.
