An oil burning furnace has many parts but at its core is a very simple machine. For a forced air oil furnace I think it’s best to think of a furnace as a two part system. The first part burns oil to produce heat. The second part pushes the heated air through a series of ducts and delivers the heated air to each room throughout a home. The two parts are separated by the heat exchanger.
To describe each part and what it does I’ll start at the beginning. The Oil Supply Line is a pipe that brings the oil from its Storage Tank and delivers it to the furnace. The oil goes through an Oil Filter before entering the Oil Pump; this pump sends the oil into the Blower. The blower is powered by a Motor that mixes the oil with air pressurizes the mixture then sends this mixture to the Burner Assembly. The burner assembly ignites this oil mixture inside the Combustion Chamber. The hot air passes though the Heat Exchanger, before exiting the house though the Flue inside a chimney. The heat exchanger which may be made of cast iron, pressed sheet metal, aluminum or other materials will get very hot.
This is where the second part of this heating system takes over. Cooled air is returned to the furnace inside the Return Air Duct by a large Blower Fan. This fan is responsible for circulating all the air throughout your home. The blower fan pushes the cooled air past the heat exchanger where it becomes heated. Finally this heated air is delivered to your home via a series of metal passages called Ducts. The air enters the room though Registers in the floor, walls or ceiling.
The process used in a gas furnace works in much the same way as an oil furnace but the ignition process/parts differ.
Gas and oil boilers burn their fuel exactly as a forced air furnace would, but the second part of the heating system differs in that it uses heated water or steam instead of air to deliver the heat to the house.