Modern Central Heating

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7 Electric Heating

Storage Radiators

 Electric storage heaters are not really central heating but we still have included them on this web site because it is an option worth considering. Storage Heaters use off-peak electricity (supplied at a cheaper night-time rate) to store heat in special heat-retaining clay blocks. These then give out heat slowly during the following day. Economy 7 and Economy 10 are both current off-peak tariffs which usually require  a second electricity meter. Storage heaters are manufactured in a range of sizes with storage capacity quoted in kWh, and a typical heater is capable of being charged at a rate of 3.4kW and able to accept a maximum charge of 24 kWh in a 7 hour charging period.

Modern, slim-line storage heaters often have a charge control (or an automatic charge control) which adjusts the amount of heat stored overnight. An automatic charge control does this by measuring the temperature in the room (or more rarely, outside the house) and if it is milder, stores less heat (saving money in the process). If the storage heater has a manual charge control, you will have to make this adjustment yourself.

Storage heaters give out their heat partly by radiation and partly by convection:
  • radiation comes from the front panel - it cannot be controlled (ie up or down)
  • the convected warm air can be adjusted by flaps above the blocks. Some heaters also have a fan to produce a heat boost; however it will also cool the heater down more quickly.

Many people who use storage radiators are quite happy with them. They are reliable, don't leak and unlike a boiler a breakdown does not disable the whole house. On very cold days supplementary heat is often required.

On some storage radiators (such as the Dimplex FXL model - left) a fully automatic charge system ensures just the right amount of heat is stored whatever the weather.  This meets the requirements of Building Regulations Part L1, which now requires all storage heaters installed in new buildings to be fitted with automatic change controls. This particular model is also wired to on-peak electricity so it can be used as a normal convector heater as well.

These radiators can get quite hot and guards are available to protect the young and the very old.

Thermal Storage

 Whereas in a traditional system the boiler heats the water for the radiators and, via a heat exchange coil, heats the water in the cylinder for the domestic hot water, an electric thermal store reverses these functions. In a thermal storage system it is the water in the cylinder which is heated by the electric boiler (mostly off-peak), then stored and maintained at a constant temperature and pumped through the radiators as required. The water for taps and showers coming from the mains supply, is heated by the hot water in the cylinder via a highly efficient plate heat exchanger and then goes on to the taps and showers - still at mains pressure. 
This offers a number of benefits:
  • The store acts as a 'cushion', with the boiler only having to meet average demand - so it is possible to install a smaller boiler.
  • The boiler will operate at close to peak efficiency. With the exceptionally high insulation levels of the thermal store ensuring that the water temperature rarely drops more than 10-15 degrees, the demands on the boiler are such that stop/start cycles are greatly reduced, producing savings in running costs.
  • The primary water in the thermal store is always available instantly at optimum temperature. Radiators are therefore heated almost instantaneously, resulting in a rapid rise in room temperature.
  • With combined units available which include an integral boiler, it is possible to take the boiler out of the kitchen and into the airing cupboard.
  • Controls are simplified as hot water programming is no longer necessary.
  • Good shower pressure
  • The capability to provide high simultaneous demands, to serve different locations at the same time
  • No cisterns or pipes in the loft, so no need to worry about freezing pipes in the winter

The graphic on the left shows the main features of a thermal storage system. Gledhill, the makers of the unit, shown on the right, also produce units suitable for oil and gas boilers.

©2006 University of the West of England, Bristol
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