Many houses are heated by burning in furnaces wood, coal, coke or other solid fuels. Before the XX century it was the usual method of heating. Subsequently, in the developed countries for heating are widely used oil, gas and electricity, because it is easier and cheaper.
Heat transfer
From the object heat can be transferred by radiation, conduction and convection or by their combinations.
In the form of heat radiation is a form of electromagnetic radiation like light or radio waves. It can pass through air and even space. Some environments, it is the air, absorb a small amount of radiation energy, skipping most of it. Others or reflecting the radiation, or absorb it. The ratio of absorbed and reflected radiation depends on the color, the composition and structure of the material. Dark and rough surfaces absorb radiant heat in greater quantities than bright and polished, which reflect most of it.
The conductivity of heat from one object to another occurs through direct contact - heat moves from hot object to cold. For example, during Ironing the heat is transferred from the iron to the fabric.
Convection - heat transfer by circulation, characteristic for liquid and gas. For example, the air heated by the radiator, it forms convection currents in the room. Heated air expands, its density decreases and it rises. Cold, heavier air takes its place and is heated by the radiator. In the upper layers of it gradually cools, giving up its heat and falls down. As a result there is a constant circulation of convection currents of air.
Various heating devices transfer heat in different ways.
During the combustion of solid fuel in fireplaces the heat is radiated into the room. Some devices heat the boiler, located in the back, to heat the water. In the water heat is transferred by convection.
Gas heaters are usually elements of the filament emitting heat. Some electric heaters have elements filament lamps with reflectors arranged behind them. Another type of electric heaters work through convection. The holes enable air to flow through the heating elements and to create indoor convective flows.
Emissions
The fuel combustion in the heaters leads to the formation of harmful gases and soot. For removal of smoke build the chimney with a chimney. When using some small gas or oil heaters to remove smoke enough ventilation.
Electric heaters do not emit smoke and do not require ventilation. In which the heat formed during the passage of electric current through the wire heating element. This does not mean that electricity is less harmful for the environment. It is often get in thermal power plants burning coal, gas or oil. Thus, the main difference with electricity is that emissions arise during its production, and not consumption.
Because electric heaters do not smoke, they are very comfortable and easy to operate. In some houses for heating used Underfloor heating in which the ceramic plates heat up electric wire elements at night, when the load on the grid is minimal, and then slowly give off heat during the day. However, the most common are heaters that use heat-retaining blocks for space heating during the day.
Concealed electric heating is a modern development, but the idea of hundreds of years. Also not a new principle of Central heating, which heat source heats a few buildings. Both these principles were used in the ancient Roman hypocaust - first the Central heating system.
Central heating
In hypocaust firewood burned in the cavity under the stone floor. Smoke and hot air circulated under the floor, rising upward through cavities in walls and passes through the top hole. In addition to heating, the furnace also heats the water for washing. Like them modern Central heating systems are used for heating and water heating. Water is an integral part of such systems. Usually gas, oil or coal are burned, heating the water, which then passes through radiators located in each room. The radiators have a large surface area to increase the amount of radiated heat. After passing through the radiator system heats up the water again.
Water from the boiler passes through a copper coil inside the tank. The coil acts as a heat exchanger, transferring the heat water supplied to the taps.
Large Central heating system provide heating and hot water for houses of the whole neighborhood. Some systems have their own boilers, while others use excess heat from power plants.
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