Electric Storage heaters use cheap overnight (Economy 7) electricity to heat a thermal mass inside the heater (typically concrete or ceramic blocks) which then release that stored heat during the day when electricity prices are higher. Some modern storage heaters are also equipped with a fan to help assist heat dissipation and ensure a more even distribution within a room.

Electric underfloor heating schematic Energy use can be optimised by regulation of the amount of energy input overnight, versus the level of heat you require “released” during the day. Most heaters have some form of these controls built-in but more modern ones can also be connected to more sophisticated external control systems.In terms purely of energy-saving, the principle of using cheap energy to create and store heat and release it during the following day is not effective:
  • Production of heat from the unit during overnight storage is unavoidable – implying:
    • Heating a room (overnight) when you do not require that heat;
    • A significant proportion of the energy consumed does not turn into heat for the next day;
  • Energy is wasted “priming” the thermal mass to a point where it will effectively emit, which cannot be recovered as useful comfort heat in the release phase;
  • Loss of stored heat in the release phase is unavoidable – implying either production of heat that you may not want (e.g. during a sunny autumn or winter’s day) or production of insufficient accumulated heat which then requires top-up (for example if the input was set too low). Either option is uncomfortable and a waste of energy.

So the only possible advantage of consuming energy for heating in this way is:

  • if it proves much cheaper relative to other forms of electrical heating that output heat directly at point of need during the day when prices are higher and
  • if thermal comfort is as good, or better than other forms of heating.

Storage heaters fail in both the above respects. They are an artefact of the 1970’s overnight capacity excess on the grid which spawned Economy 7 and a push to find appliances that could use it. Given the pricing policy and technology of the time, storage heaters made great sense.

These days the poorer Economy 7 savings (offset by higher daytime rates); the innefficient way the heat is created, stored and released and the poor levels of comfort produced from storage heaters significantly fail to match the lower daytime running costs and greater comfort levels of modern Herschel Infrared panels.

Installation considerations:

Storage heaters tend to be large units because of the size of the storage media and room space must consequently be sacrificed in order to place the units against a wall and avoid placing furniture too close.

Before the advent of units with internal fans, a zone surrounding the heater was also uncomfortably hot. The fan gets around this, allowing more even dissipation of the heat, however it does imply a further energy overhead and cost during the more expensive daytime rates – which goes against using the storage/Economy7 principle in the first place.

Purchase & Installation costs:

Storage heaters can cost between 200 – 500 UK pounds, overlapping in cost with Herschel Infrared panels required for similar areas, although bigger storage units will be marginally cheaper than the equivalent bigger infrared panels.

Installation costs for storage heaters are greater than for Infrared panels because of their greater weight and size.

Because of the greater power consumption of storage heaters, operation of several simultaneously will require a correctly loaded electrical circuit separate from other household appliances. This requirement is unlikely to obtain with Herschel Infrared heaters unless many were to be used simultaneously on the same circuit.

Operating Costs:

For a room of 50m3, a 2.6kW storage heater running at full charge for the 7 hours (hence “Economy 7”) at an average rate of 8 pence per hour will cost 1.45 pounds a day. (You could run the heater with less charge but get less heat output the following day).

For the same room, you will only require 1.2kW Herschel Infrared (for example two 600W panels) which will cost 1.17 pounds for 7 hours on daytime rates. It is likely you will actually require 5 hours running a day or less – especially if you have two 600 Watt heaters – because your thermostat can control the Herschel Infrared usage precisely. However 7 hours at least shows a running-time cost-comparison with the storage unit and the Infrared still comes out cheaper even on daytime rates – producing heat only as you want it.

In a typical case study we performed, a 3 bedroom house with double-glazing and cavity walls and previously heated using “Night Storage” heating experienced the following energy-savings.

Cost comparison between storage heating and Infrared
Cost comparison between storage heating and Infrared

Breakdown of what we replaced:

Night Storage Energy Requirements Infrared Requirements
Night Storage Energy requirements Infrared energy requirements

These are substantial savings made in a real-life scenario and go to show the impressive efficiencies implied by this new technology.

Advantages of storage heating:

  • Uses cheaper-rate electricity;
  • Releases heat gradually through the day;
  • Can be easily installed where it is impossible to have fossil-based heating or other alternative heating solutions like Biomass or heat pumps (e.g. blocks of flats);

Disadvantages of storage heating:

  • Difficult to predict next day’s heating requirements the night before, when controls are set;
  • Cannot have the right comfort at “point of need” either by turning on or turning off;
  • Heat cannot be stored indefinitely and will dissipate even if the unit is “off”;
  • Heat cannot be “zoned” to where it is required. This is a very important principle of energy-efficient comfort heating: you want the warmth where it is needed. You shouldn’t have to have heat and pay for it where you don’t need it. You also need to be able to warm up or cool down as you require it. A heater that is always on; hard to regulate and unavoidable is stuffy and expensive, not comfortable and energy-efficient;
  • Economy 7 does not give substantial enough savings to make-up for the energy-inefficiency of storage and the uncontrollable levels of comfort produced over the day when compared with many other forms of electrical heating, including heat pumps or Infrared that run during the day and can be much more precisely controlled;
  • Daytime electricity rates for Economy 7 or similar off-peak savings schemes are often higher than they are with no off-peak scheme in place – meaning all your other daytime appliances could be consuming more than the savings made from the few items running overnight Economy 7;
  • Payback times – when compared to infrared – are longer, because storage costs more to install and much more to operate.

Herschel Far Infrared Heating as an alternative to storage heating:

  • Herschel Infrared uses electricity to produce heat only as it is needed to warm people and warm-up the thermal mass of the building. Some well known brands of Infrared heater claim to have “semi-storage” cores, but Herschel does not advocate this as a design philosophy. Herschel Infrared heaters do not consume additional energy to prime and maintain a storage medium in the hope this is of some residual use when the current is switched off. Herschel believes all energy should be emitted directly and the only useful thermal mass is the fabric of your building, which warms and retains warmth over time;
  • Herschel Infrared purchase prices are comparable to many storage heaters, although the larger wattage Infrared heaters will be more expensive than comparable larger wattage storage units – but the price differential will be quickly offset by storage installation prices and higher running costs of storage;
  • Herschel Infrared is significantly easier and cheaper to install than storage heaters;
  • Herschel Infrared is cheaper to run than storage heaters;
  • Herschel Infrared is easier to zone – storage heating cannot be zoned.

 

Publisher: Herschel Far Infrared