An oil filled radiator, also often known as a column heater, is a common form of convection heater used in domestic heating.
Oil heaters consist of metal columns with hollow cavities, inside which oil flows freely around the heater. A heating element at the base of the heater heats up the oil, which then flows around the cavities of the heater by convection. The high specific heat capacity allows the oil to store a large amount of thermal energy in a small volume, while the high boiling point allows it to remain in the liquid phase for the purpose of heating, so that the heater does not have to be a high pressure vessel.
Using the oil as a heat reservoir, the heating element heats the oil, which remains warm for a long period of time while the heat is transferred to the metal wall through convection, through the walls via conduction, then to the surroundings via convection and radiation. 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 rapidly from the heater into the room.
The Efficiency
Although oil heaters are more expensive to run and provide far less spatial heating than gas heaters, they are still commonly used in bedrooms and other small-to-medium-sized enclosed areas. This is because gas heaters, especially when unflued, are not suitable for bedroom use – gas heaters cannot be used in confined spaces due to the reduced oxygen and emissions produced. This leaves electrically powered heaters, such as oil heaters and fan heaters, as the only alternative.
There are several efficiencies that can be measured in regards to heaters: the efficiency of the heater at converting electricity to heat, the efficiency of heating a room with a given amount of power may also be measured. The efficiency of the electrical generator which powers the heater and power loss from transporting the electricity over power lines may be measured also. Measures may also consider how well a heater keeps the temperature of a space above a certain point.
In general, oil heaters are considered safer than electric fan heaters, as they can have lower surface temperatures and require less consideration of the flow of air through/over the heater.
Most modern small heaters have some form of tilt sensor to cut power if they are knocked over or placed on an unstable surface. This can reduce the risk of fire if a heater is knocked over.
Typical oil heaters range in power consumption/output from 300 to 2400 Watts, and their length and number of columns is roughly proportional to their power rating. A 2400 Watt oil heater is usually approximately 1 metre (3.3 feet) in length.