During the 1960's, when oil was relatively cheap, oil heaters became very popular. Oil may be easily stored in small tanks, flowing by gravity from tank to burner.
Heat distribution can be achieved by both convection (often fan assisted) and by radiation.
Oil Heaters fall into two categories:
Flued :Where the products of combustion leave the room via a chimney or flue.
Flueless: Where the products of combustion remain in the room.
Most flued oil heaters are of a size suitable for "open living" lifestyles, that is, two or three rooms forming a large space. These larger oil heaters are usually mounted against the wall and are permanent fixtures. Because flued heaters allow the products of combustion to escape from the room with a consequent loss of heat, they operate at about 75% of efficiency.
Small heaters burning kerosene are often flueless. The flueless heater allows all the heat to enter the room, but the hydrogen in the kerosene combines with oxygen in the air to form water. This results in a high
moisture content in the room in winter. This can damage paint on window sills and can lead to mildew problems in badly ventilated areas, particularly in adjacent unheated rooms with no ceiling insulation.