the minimum "closed" setting corresponds with "early" and the maximum "open" setting corresponds with "late". These output switches can be controlled manually by ensuring they are closed at night and opened when desired, or they can be left to automatic operation by not closing at night. Thermostatic controls A thermostatic storage heater will automatically regulate the temperature in a room throughout the day. However, the operator may wish to switch the thermostatic switch to the minimum setting overnight to lower the room temperature. If the room is empty during the day, it is better to keep the thermostat at the minimum setting and then increase the setting when the room is occupied in the evening. Some thermostatic heaters also make use of on-peak electricity when there is not enough stored heat to maintain the requested temperature; the user may wish to be aware of this and lower the settings. Fan-assisted storage heaters Fan-assisted storage heaters employ an electric fan to drive air through the heater rather than relying on convection. The fan is usually controlled by a thermostat which allows the user to set the desired room temperature. The use of the fan means these heaters can be insulated more than other models, and therefore lose less heat due to heat transfer at times when heat is not required (such as when the room is not occupied, or at night). Environmental aspects In common with other forms of direct electric heating, storage heaters are not necessarily environmentally friendly because the source of electricity may be generated using fossil fuels, with up to two-thirds of energy in the fuel lost at the power station and in transmission losses. 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 and Germany have banned the installation of electric space heating in new buildings for similar reasons (though in Germany the ban was lifted in 2013). In the UK, a storage heater earns a "Poor" rating for Environmental Performance on an Energy Performance Certificate. However many progressive countries are developing their electricity generating system, principally, to incorporate "greener", more sustainable and renewable energy sources; so how "green" a storage heater system is would in principle depend on how the electricity used is generated. Of course this argument applies to all forms of electric