How do electric heaters work and which variants are available?

Electric heating is experiencing a renaissance 

Some people certainly still know the old night storage heaters that were installed in the 1950s and 1960s as an alternative to stoves for coal or heating oil. During the so-called off-peak phases of the electricity grid, especially at night, the electric current was used to heat up the storage heaters. The heat generated was kept there for several hours. 

Due to the oil crises in the 1970s and the resulting increase in energy costs, as well as the reduction of subsidies for night-time electricity tariffs, storage heaters became less economical than conventional central heating systems.

The supposed end of night storage heaters was decided in 2009 by the then German government in the Energy Saving Ordinance (EnEV). This prohibited the use of night storage heaters with a transitional period. However, this decision was revised again in 2013. ^(*1)

For some years now, however, electric heating systems have been experiencing a renaissance and are once again being used more frequently as an alternative to gas and heating oil. The reasons for this are complex, as some fundamental factors have changed.

• The efficiency of the various electric heating solutions has increased significantly compared to the previous night storage heaters.
   
• The heat demand in new buildings and renovated properties has decreased enormously due to better insulation. 
   
• The limited availability of fossil fuels such as gas and heating oil continues to cause prices to rise.
   
• Political unrest, such as the current conflict in Russia and Ukraine, is also leading to a reduced supply and higher costs for fossil fuels.
   
• According to the current federal government, the installation of gas heating systems is to be banned from 2024. However, a final decision has not yet been made (as of 07/2022).
   
• The reduced feed-in tariff for photovoltaic systems (currently 6.24 cents per kilowatt hour) ensures increasing self-consumption of the power generated. ^(*2)
   
• The continuing trend towards compact living - keyword "Tiny House" - requires new, equally compact heating systems.
   

Electricity becomes heat

If we look at heat generation from a physical point of view, the law of heat of electricity, also known as the first law of Joule, plays the decisive role. To put it simply, this law describes a continuous heat energy that is generated by an electrical conductor through which current flows.

Applied to electric heaters, this means that, for example, a heating rod, a heating cable or a heating film have current flowing through them and thus generate heat energy.

Some electric heaters primarily heat the room air, which is referred to as convection in technical jargon. Examples of convection heaters are radiators, fan heaters or convectors. However, since air is considered a rather poor heat carrier, the operating costs of such systems are sometimes very high.

With other electric heating systems, radiant heat predominates. Here, it is mainly the objects in the room that are heated and not the air. Infrared heaters or electric underfloor heating systems are examples of this. The operating costs are usually significantly lower compared to convection heaters. 
 

Convectors

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Radiators

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Fan heater

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Infrared heating panels

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Heating film

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Heating mats

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Heating film, fleece-laminated and perforated 

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But how much power is actually needed?

Exactly how much power is needed depends heavily on the so-called heating load of the property. The heating load, formerly also referred to as heat demand, is the required heat flow (heat supply) that ensures the desired room temperature at the lowest local outdoor temperature in winter. The energy certificate, which has been compulsory since 2009 for new buildings, resales of houses and flats, as well as for new leases, contains this information.

If no corresponding energy certificate is available, a rough estimate can be made using the following guide values:

• 120 W/m² old building, without special thermal insulation
• 60 - 100 W/m² building with normal thermal insulation
• 40 - 60 W/m² New building according to the Thermal Insulation Ordinance 1995
• 30 - 50 W/m² new building according to heat insulation ordinance or EnEV 2002

In bathrooms, a surcharge of 10 percent should be calculated, because a room temperature of 24°C is considered the standard here. For the other rooms, 20°C is assumed to be the standard temperature. ^(*3) 

Another important role for the economical operation of an electric heating system is its correct operation. Programmable thermostats with temperature-controlled regulation are particularly suitable for this purpose. This means that the heating regulates itself downwards when a certain room temperature is reached. The time periods and temperatures can be easily adapted to individual needs. 

For stationary electric heaters, such as infrared heating panels, electric floor or ceiling heaters, the EU Ecodesign Directive 2015/1188 also applies. This describes that, since 01 January 2018, the installation and commissioning of these heating sources is only permitted in conjunction with external thermostats that have electronic room temperature control, weekly programming, adaptive control or open window detection.

Many modern room thermostats can even be integrated into an intelligent home control system - so-called smart home systems. This allows demand-oriented control of the heating via an app or even fully automatic lowering of the temperature when leaving a previously defined area with the help of the location transmission (geofancing) of the smartphone.