Filtration, Atomization and Combustion

While oil-burning furnaces differ in specific details of operation from model to model, most follow a similar cycle of operation. Heating oil is kept in a large storage tank, outside of the home, that is connected to the indoor furnace by a pipe. An oil-burning furnace goes into operation each time its thermostat (located elsewhere in the house) signals that the temperature has dropped below the desired temperature. A fuel pump sends oil through the pipe, passing it through a filter en route to the combustion chamber. In order for the oil to burn properly for heating, it needs to be mixed with air as an oxidizer. This is done through the process of atomization. A regulating valve sprays a mist of oil through a nozzle into the combustion chamber, where it is mixed with air and ignited by a spark from the ignition system of the furnace. As the combustion chamber rapidly heats up, a shared metal wall conducts heat between the combustion chamber and an adjacent chamber called the heat exchanger.

Distribution of Heated Air Throughout the House

As the air in the heat exchanger reaches a certain temperature, a blower begins to force the heated air out through a system of ducts that lead to each room of the house. To replace it, cold air is returned to the furnace from ducts in each room that are part of a separate return system. The returning air passes through an air filter so as to keep dust and suspended matter out of the furnace blower. After being heated in the exchanger, the air is circulated by the blower into the rooms of the house through the heating ducts, which are typically hand-adjustable either on the grilles in each room or (in older installations) by using valves in the ductwork closer to the furnace. Once the thermostat signals that the temperature has risen to the selected level, the atomization and combustion process in the furnace is halted. Since hot air remains in the ducts, however, the fan keeps blowing for a preset period of time to ensure that all of the warmed air reaches the rooms. This is the reason why, when the furnace begins blowing again on its next cycle, the air coming out of the vents is initially cool.

Emissions

From the combustion chamber, the by-products of the burnt oil and air mixture rise up a chimney to be vented into the air. These emissions consist primarily of carbon dioxide, nitrogen and water. In recent years, oil-burning furnaces have become far more efficient than earlier models. The flame retention burner, introduced in the 1960s, burns up to 15 percent more efficiently with a smaller, hotter flame and also directs the air more closely for an optimal mixture with the oil. More recent advancements include electronically-controlled high static air pressure to control accumulation of particulate matter, which is claimed by manufacturers to decrease particulate emissions by as much as 95 percent.