A storage heater is an electrical appliance that stores heat at a time when base load electricity is available at a low price, usually during the night, and releases it during the day. Heat is usually stored in clay bricks or other ceramic material because of the low cost and high specific heat capacity of these materials. Storage heaters are usually used in conjunction with a two-tariff electricity meter, which records separately the electricity used during the off-peak period so that it can be billed at a lower rate. In order to derive any benefit from a storage heater, the house must be on a special electricity tariff.
Storage heaters usually have two controls—a charge control (often called input), which controls the amount of heat stored, and the draught control (often called output), which controls the rate at which heat is released. In many models these controls are set manually. Other models are automatic and allow the user to set the target room temperature using a thermostat. Many units also contain a conventional electric heater, which can be used to give a boost in heat output during the day. If this feature is relied upon too much, a lot of peak time electricity will be used and the storage heater will prove expensive to run.
Storage heaters have several drawbacks:
- If insufficient heat has been stored, for example if there is an unexpected period of cold weather, then any extra heat needed will have to be produced using full-price electricity.
- If too much heat has been stored, then sooner or later the heat will be released into the room whether it is needed or not.
- Storage heaters are very heavy and somewhat bulky, due to the material used to store heat.
- Unless the heater is of the modern well-insulated type, heat is leaked out whenever the bricks are hot, meaning that having a room warm in the evening requires it to be warm all day (albeit probably at a lower setting). However, the consequences of this energy loss are often more than compensated for by the heater’s use of an off-peak base load that is effectively "spare energy" and is cheap.
Storage heaters have declined in popularity due to the drawbacks and due to the low cost of gas-fired central heating. However, many new properties in the UK are built with storage heaters, and their inspection and maintenance costs are less than those of gas heating.
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Using Storage Heaters
Storage heaters can be very cost effective if used properly. However, some thought and planning are involved in understanding the heater’s mode of operation and using the heater effectively throughout the year.
Power Switches
Newer installations will provide two separate power circuits, one for on-peak and one for off-peak electricity, and two power switches on the wall next to each storage heater. These should be switched off during the summer when the operator does not require heat. During other months the off-peak switch can be left on at all times, with the on-peak switch being used when insufficient energy has been stored during off-peak times. The amount of heat that is stored can be altered using the controls on the storage heater unit.
Basic Controls
Basic storage heaters have an input switch and an output switch (also called the heat boost on some models).
The position of the input switch should be changed to reflect how cold the night and following day is predicted to be. The input switch is normally thermostatic, controlling the maximum temperature that the bricks are allowed to heat to overnight. The exact setting needed will depend on the desired room temperature, the number of hours in the day that the temperature needs to be maintained, and the room’s rate of heat loss under a given set of circumstances. Some experimenting may be needed to find the relationship between forecast outside temperature and best input setting for a particular room. Most storage heater users follow simpler guidelines; for example, in the middle of winter, it is often appropriate to turn the input switch to its maximum setting. There is no need to touch the input switch on a daily basis if you are expecting the same sort of weather for weeks at a time. There is no need to touch the input switch during the day, as storage heaters only use electricity overnight when it is cheaper.
The output switch does require attention throughout the day. Before going to bed, the user should switch the output to its minimum setting. This keeps as much heat in the bricks as possible. Enough will leak out into the room to make it warm in the morning. Only in exceptionally cold circumstances will the operator require output overnight. The operator may wish to slowly increase the output switch during the day to try and maintain the temperature in the house. Increasing the output will allow the heat to convect out of the heater. If the house is empty during the day, the output should be left at a minimum all day and then switched up when the occupants return home to let more heat escape into the house.
Thermostatic Controls
A thermostatic storage heater will automatically regulate the temperature in a room throughout the day. However, the user may wish to switch the thermostatic switch to the minimum setting overnight to stop the room being kept at an unnecessarily high temperature overnight. If the room is empty during the day, it is better to keep the thermostat at the mimimum 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 desired temperature; the user may wish to be aware of this and lower the settings.
Environmental Aspects
In common with other forms of direct electric heating, storage heaters are not normally considered environmentally friendly because most electricity is generated remotely 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, while Denmark has banned the installation of electric space heating in new buildings for similar reasons. Many progressive countries are developing their electricity generating system, principally, to incorporate "greener," more sustainable, and renewable energy sources.
In some countries, the current design of the electrical generating system may result in a surplus of electricity from base-load power stations during off-peak periods, and storage heaters may then be able to make use of this surplus to increase the net efficiency of the system as a whole. However, future changes in supply and demand—for example as a result of energy conservation measures or a more responsive generating system—could reverse this situation, with storage heaters preventing a reduction in the national base load. Other future technologies, however, incorporate electricity-supply-sensitive electronics to sense when there is a change in supply and demand. Thereby, they ensure that these loads only use off-peak electricity.