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An electric heater is a device used for heating rooms or spaces. This particular model of the electric heater was found amongst other treasures at the Mooreland Annex in Melbourne, Australia. This beautiful relic is reminiscent of the old broadcasting microphones that came to be the symbol of radio in the 1930s. It also resembles the traditional steel fans with their menacing metal grille tempting the fingers of the young with ghastly results. One of the most striking elements of this old electric heater is how dangerously unstable it looks, this little heater threatened to topple over and set the place alight.
Technically speaking the electric heater is an electrical appliance that converts electricity into heat utilising the principle of Joule heating. Joule heating is the process in which electric energy is converted into heat energy by an electric current flowing through a resistor. The process works as the resistors become hot when an electrical current is sent through them and meets resistance. Resistors may be composed of metal-alloy wire, non-metallic carbon compounds, or printed circuits. Heating elements may have exposed resistor coils mounted on insulators, metallic resistors embedded in refractory insulation and encased in protective metal, or a printed circuit encased in glass. Fins may also be used to increase the area that dissipates the heat. This particular early model of heater has a porcelain cone that contains a heating coil positioned in the middle of a metal disc.
All electric heaters utilise the same physical principal to generate heat, however there are several different methods by which the heat may be delivered.
Radiant heaters, or “space heaters”, contain a heating element that reaches a high temperature and a reflector to direct the heat away from the body of the heater. The heating element is generally packaged inside a glass envelope resembling a light bulb that emits infrared radiation. The infrared radiation travels through the air until it reaches an absorbing surface at which point the energy is partially converted to heat and partially reflected. Radiant heaters directly warm people and objects as oppose to heating the actual air itself, this is known as ‘direct heating’ or ‘spot heating’. Due to this method of direct heating radiant heaters are used efficiently in areas of higher airflow. This style of heating is an excellent choice for task specific heating and is used for industrial purpose. However due to the focused intensity of their output and general lack of overheat protection, this direct heating poses great potential danger to nearby furnishings.
A convection heater delivers the heat energy via conduction. The process of conduction is based on the principal that hot air is less dense than cold air. The heat energy is transferred to the air surrounding the heater thus decreasing the density of the air causing the hot air to rise. The cool air replaces the rising hot air and is in turn heated. As the hot air rises it becomes distanced from the heat source and eventually cools and falls. This heating and cooling creates a constant current of hot air that leaves the appliance through vent holes and heats up the surrounding space. Convection heaters therefore work best in a closed space and are very safe posing a low risk of fire hazard. In the United Kingdom, these appliances are sometimes called electric fires, because they were originally used to replace open fires.
A fan heater is essentially a convection heater with an electric fan which speeds up the airflow. This reduces the thermal resistance between the heating element and the surroundings, allowing heat to be transferred faster. However they are considerably noisy due to the fan and do pose a higher risk of fire hazard, although the risk is moderate.
A storage heating system utilises cheaper electricity sold during low demand periods. The heater stores the heat in clay bricks and releases it when required during the day.
The most consistent room temperature is achieved by a home radiant heat system works by running an electric current through a conductive heating material which then heats the flooring to the temperature set by the thermostat. The flooring then heats the adjacent air which, as it rises, heats the room and its objects by convection.
Electric heaters are utilised in materials processing in industry and the joule principle is adapted for many of our day-to-day appliances including the hairdryer and toaster both which employ the use of resistors to create heat. The electric heater is a source of direct heating as the conversion of energy into heat occurs at the site to be heated. Due to this they are generally used as a domestic or personal heater often small and easily transportable as central heating is a much more cost effective and consistent method of heating large spaces and home.
However, the concept of central heating is not a new one. The earliest methods of indoor heating appeared when man discovered fire, the humble campfire has provided man with warmth for millions of years. Many Asian and Mediterranean countries with milder climates also used fire to heat spaces but they tended to use charcoal, made from burnt timber, for fuel as oppose to wood as it created less smoke. The problem of the excesses of smoke from burning materials in a confined space was virtually eliminated by the 13th century after the introduction of the chimney to Europe. Initially a simple hole or aperture in the ceiling the chimney soon found its home directly above the fireplace.
The ancient Greeks on the other hand are believed to have invented and utilised an ingenious method of central heating not dissimilar to that employed today. But it was the Romans who engineered the heating system known as hypocaust. The system was essentially a collection of air spaces or ducts that were located beneath the mosaic floors. Brushwood, charcoal or coal was burned at a central location and the hot air travelled beneath the floor heating it. This system of heating disappeared with the Roman Empire, emerging 1500 years later.
The experimentation and development of the light bulb in the late 1700s revealed that heat was created when electrical current was passed through resistors. This creation of heat was a great obstacle in the development of the light bulb but allowed for the development of many other appliances and industrial methods. The electric heater was created around 1822, the year the French mathematician Jean-Baptiste-Joseph Fourier published a mathematical description of the laws of conduction that were formulated by French physicist Jean-Baptiste Biot in 1804.
The original electric heaters were similar to the one pictured in that they were small and unsteady looking appliances that whilst getting very hot themselves did not deliver much heat to the surrounding areas. This posed a big problem as the only way to attain warmth from the heater was to sit as close to the heater as possible which in turn resulted in innumerable house fires and burns, in particular in the 1950s. However, although the design and safety of the electric heater has been developed over the years and central heating has become extremely common the fire hazard posed by electric heaters has not disappeared.
In a modern day setting the risk posed by electric heaters is generally due to misuse. A common misuse of the electric heater is when small space heaters are employed to heat large spaces and are left unattended or are consistently used for prolonged periods. This is a particular issue in places that experience extreme cold, such as Europe. Many of the modern hazards posed by the electric heater are the same as any other electric appliance which requires maintenance of electric cords. Other hazards are posed by inadequate vacant space surrounding the heater causing ignition of furnishings or papers. Drying clothes or hanging things over heaters also creates a potential hazard.
As the design and efficiency of the electric heater increased the modern home saw a steady decline in the use of the messy old fireplace and even the aesthetic value of the traditional was traded in for the removal of the chimney draught. However nowadays we are seeing a return of the aesthetic value and sensory comfort of the humble fire. Electric fires and gas fires are becoming an increasingly popular addition to the modern home in combination with a hidden central heating system.
With a strong social focus nowadays on sustainability and energy efficiency society has seen a rapid decline in the presence of the electric heater. The trend has shifted to building houses that require minimal heating due to effective insulation among other things. However the basic principle upon which the electric heater works will remain in other appliances for a long time to come but one day we will have to return to the campfire for that familiar feeling of being so close to direct heat that you feel as though you are burning but when you step back being overcome with a rush of coldness. This is what electric heaters mean to most of us when they evoke those memories of cold nights and warm pyjamas from our childhood.
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