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Efficiency in electric heating

Efficiency is a widely misunderstood term when it comes to electric heating. The fact is that electric energy is converted to heat with 100% efficiency at the point of use.

Therefore the actual efficiency of an electric heater – any electric heater – is 100%.

If you pay for 1kWh of electricity, 1kW of heat will be transferred into the room for one hour. This is dictated by one of the principal laws of physics, The Law of Conservation of Energy – “Energy cannot be created or destroyed, but can only change from one form to another.”

However while it is true that all electric heaters are 100% efficient, they don’t all operate in the same way.

For example an oil (or thermodynamic fluid) filled radiator has different performance characteristics to a panel convector heater.

The fluid in the radiator will transfer the heat uniformly around the radiator giving a higher proportion of radiant as opposed to convected heat in comparison to a convector heater. This is useful for certain applications, however the very small thermal storage capacity of a fluid filled radiator also results in slow release heat to the room during start up and a slightly prolonged release of heat to the room after switching off.

By comparison a radiator or panel convector heater with no fluid would release heat to the room more quickly during start up and stop releasing heat more quickly at “switch off”.

Importantly in both cases they release exactly the same amount of energy to the room.

The European Commission Study of Local Room Heating products (DG Ener Lot 20) states: “Since the ‘heat generation efficiency’ is always 100%, it does not allow comparing the energy performance of electric room heaters.”

The government’s standard assessment procedure for energy rating of dwellings (SAP 2012 Version 9.92 Dec 2011) draws no distinction between panel, convector or radiant heaters, water or oil filled radiators, fan heaters or portable electric heaters – each has an efficiency of 100% and a responsiveness of 1.