Local heating systems
Central heating is more common in the United States than in most other countries. Local heating is still in common use in many countries. Such heating comes from fireplaces, wood-burning stoves, or room heaters. The earliest type of local heating system was the open fire within an enclosure, such as a cave or a tent. Such a fire is not satisfactory because the area soon becomes filled with smoke. Also, an open fire without a chimney lacks enough draft to burn brightly.
If a fireplace is put at one side of a room and provided with a chimney, the smoke and combustion gases will pass up the chimney. The chimney provides a draft by which the air enters the front of the fireplace and passes up the chimney to aid the burning of the fuel. However, this draft reduces the energy efficiency of a fireplace. A typical fireplace allows enough warm air to escape through the chimney to empty an average room every few minutes. This air leak may waste almost as much heat produced by the house's central heating system as is provided by a fireplace.
Wood-burning stoves were widely used in the United States for cooking and heating before the development of gas and electric ranges and central heating systems. In the 1970s, such stoves again became popular due to the energy crisis. They were used most in rural areas of the Western and Northeastern states. In these areas, where wood is plentiful, wood-burning stoves may provide a cheaper source of heat than heating oil. But air pollution caused by smoke from wood- burning stoves has become a problem in some places.Most wood-burning stoves are made of heavy castiron or steel. Combination stoves, which resemble the stove invented by the American inventor and statesman Benjamin Franklin in the 1740s, fit into a fireplace. They have doors in the front that are used to control the draft. Such draft control enables the stove to burn wood more efficiently than an open fireplace can. In addition, when the stove becomes hot, it holds the heat better than afireplace does. Free-standing stoves operate in basically the same manner as combination stoves. But they art not attached to a fireplace.
Room heaters. Some room heaters burn gas to produce heat These can be placed in a corner of the room and used with a fan to circulate the heated air. Such heaters should not be used without adequate venting the outside because combustion gases can be harmful to the occupants of the room. Other room heaters burn kerosene and must also be vented.
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Electric room heaters pass an electric current a series of wires. These wires resist the electricity become red hot. Such electric heaters give off heat by radiation and convection. Many electric heaters are in such places as bathrooms, bedrooms, and workshops. Most local sources of heat are relatively hot, compared with steam and hot-water radiators. For this reason they produce a larger proportion of radiant heat. When such large amounts of radiant heat are used temperature of the air in the room need not to become so hot. For example, a resistance-type electric heater a quartz heater warms anyone in the path of its heat rays. But the heat rays do not significantly warm the air through which they travel.
1. Study the following words:
Enclosure, chimney, leak, draft,combination stoves,free-standing stoves, wire,
quartz heater, provide, electric current
2. Complete the sentences with appropriate words from the text:
a) Most …….. stoves are made of heavy castiron or steel.
b) …….. operate in basically the same manner as combination stoves.
c) Electric room heaters … an electric current a series of wires.
d) However, this … reduces the energy efficiency of a fireplace.
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