1) Barrel-shaped device 2) Small room-warming device 3) Solution for poor insulation 
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, such as kerosene – the oil is used as a heat reservoir (buffer), not as a fuel. ==How it works== O...
[n] - heater that burns oil (as kerosine) for heating or cooking
oilstove noun heater that burns oil (as kerosine) for heating or cooking