Oil heater

An oil heater, also known as an oil-filled heater, oil-filled radiator, or column heater, is a common form of convection heater used in domestic heating. Although filled with oil, it is electrically heated and does not involve burning any oil fuel; the oil is used as a heat reservoir (buffer).

Function

Oil heaters consist of metal columns with cavities inside, where heat-transfer oil flows freely around the heater. A heating element at the base of the heater heats the diathermic oil, which flows around the cavities of the heater by convection. The oil has a relatively high specific heat capacity and a high boiling point. The high specific heat capacity allows the oil to effectively transfer thermal energy from the heating element, while the oil's high boiling point allows it to remain in the liquid phase for heating, so that the heater does not have to be a high-pressure vessel.

The heating element heats the oil, which transfers heat to the metal wall through convection, through the walls via conduction, and then to the surroundings via air convection and thermal radiation. The columns of oil heaters are typically constructed as thin fins, such that the surface area of the metal columns is large relative to the amount of oil and element that provides the warmth. A large surface area allows more air to be in contact with the heater at any point in time, allowing for the heat to be transferred more effectively, which results in a surface temperature that is safe enough to touch. The relatively large specific heat capacity of the oil and metal parts means this type of heater takes a few minutes to heat up and cool down, providing short-term thermal storage.