 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 which 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 a short-term thermal store.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.