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Although they all use the same physical principle to generate heat, electric heaters differ in the way they deliver that heat to the environment. Several types are described in the sections below.
Radiative heaters contain a heating element that reaches a high temperature. The element is usually packaged inside a glass envelope resembling a light bulb and with a reflector to direct the energy output away from the body of the heater. The element emits infrared radiation that travels through air or space until it hits an absorbing surface, where it is partially converted to heat and partially reflected. This heat directly warms people and objects in the room, rather than warming the air. This style of heater is particularly useful in areas which unheated air flows through. They are also ideal for basements and garages where spot heating is desired. More generally, they are an excellent choice for task-specific heating.
A fan heater is a variety of convection heater that includes an electric fan to speed up the airflow. This reduces the thermal resistance between the heating element and the surroundings, allowing heat to be transferred more quickly.
A storage heating system takes advantage of cheaper electricity prices, sold during low demand periods such as overnight. In the United Kingdom, this is branded as Economy 7. The storage heater stores heat in clay bricks, then releases it during the day when required.
These systems are called radiant heating systems, regardless of whether they include a heat exchanger (also called a radiator) or are electrically powered.
The overall energy efficiency of direct electric heating is usually low. Most electricity is generated remotely using fossil fuels. The efficiency of generating electricity from combustion of fuels is typically only 30 to 40 percent. Thus even with a 100% efficient electric heater, the amount of fuel needed for a given amount of heat is much more than if the fuel was burned in a furnace or boiler at the building being heated. In Sweden the use of direct electric heating has been restricted since the 1980s for this reason, and there are plans to phase it out entirely - see Oil phase-out in Sweden - while Denmark has banned the installation of electric space heating in new buildings for similar reasons.
The operation of electric resistance heaters to heat an area for a long period of time is generally considered to be costly. However intermittent or partial day use can be more cost efficient than whole building heating since there savings due to superior zonal control.
According to Joule's Law, the heat power produced by a resistor is:
