How a Home Furnace Works
Furnaces keep our homes warm and comfortable in the winter months. Various designs make use of different kinds of fuel - oil, propane, coal, wood, natural gas or electricity. Modern types of furnaces commonly use natural gas because it is relatively cheaper and more available. In areas where electricity is affordable, home-owners may prefer electric furnaces, as these do not use combustion, and therefore, have no emissions. The following describes the basic process by which furnaces heat our homes. Does this Spark an idea?
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Thermostat
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This device monitors the temperature inside a house and is connected to the furnace. There is a pre-set level on the thermostat. Once the temperature inside the house drops below this pre-set level, the furnace automatically ignites, and begins burning the gas to create heat.
Burner
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The burner is where gas is fed and burned, and is housed in the combustion chamber. There is a small flame kept alight beside the burner called the pilot light which ignites the gas. A less wasteful alternative to the pilot light is an electronic ignition system which uses electrodes to create sparks that will light the gas coming through the burner.
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Heat Exchanger
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The hot gas from the burner moves into the metal recesses of the heat exchanger. This action is made possible by the negative pressure created by a draft inducer, which is basically a fan that moves air through the whole furnace system. When the hot gas fills the chambers of the heat exchanger, the heat is transferred to the metal casing, and then into the air flowing around it. The draft inducer's blower will push the now warm air into the ductwork for distribution to the whole house.
Furnace systems that use draft inducers are called forced-air furnaces. Older furnaces, called gravity furnaces, do not induce air movement. These obsolete furnaces are usually located in basements, and distribute warm air by simply allowing it to rise and seep into the rooms of the house through large ducts.
Electric furnaces, on the other hand, use a different method of heating the air. Electric heating components heat the air which is then pushed into the ducts by a blower. Such types of furnaces are easier to install as they are smaller, and have no need of an exhaust pipe, but they are subject to power interruptions.
Ductwork
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Ductwork is the whole array of metal ducts that run through the house, and carries and distributes the warm air to the various rooms of the house. They are typically wrapped with insulating materials to keep the heat in. The air warmed by the heat exchanger moves through the connecting plenum space, through the ducts, and into the rooms of the house. In a forced-air furnace, the ductwork also serves to carry the cool air in the house's rooms back into the heat exchanger to be heated once again.
Flue
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The flue is the furnace's exhaust pipe. Gas-fueled furnaces use combustion to generate heat, and thus, byproduct emissions such as water vapor and carbon dioxide are also generated. These are vented out through the flue. A conventional flue set-up has this exhaust ventilation pipe run up to the house's roof and release its exhaust like a chimney. In a forced-air system, the cooled gases in the heat exchanger are pushed into the flue by the draft inducer blower.
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