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A space heater is a device used to heat a single, small area. In contrast, central heating is used to heat many connected areas, such as all the rooms in a house. Space heaters are powered either by electricity or by a burnable fuel like natural gas, propane, fuel oil, or wood pellets. Portable space heaters are usually electric because a permanent exhaust is needed for heaters which burn a fuel.
Space heaters are powered by either electricity or the combustion of a flammable fuel.
Electric space heaters fall into three main categories:
- Convection heaters pass electricity through a heating element, causing the heating element to become hot. These elements are made from either metal or ceramic, and the overall process is called Joule heating. Next, this heat is transferred to the air in the room by convection. Some heaters include a fan to increase air circulation, while other heaters do not. For example, oil-filled space heaters do not have fans.
- Infrared heaters also pass electricity through a conductive wire, causing the wire to become very hot. However, most of the heat is transferred by radiant heating, and not by convection, in this type of space heater. The hot wire emits infrared rays which transfer heat directly to a solid surface, not the surrounding air.
- Heat pumps use the same process as refrigerators and air conditioners, but in reverse. Whereas convective and infrared heaters actually make more heat from electricity, heat pumps only move the location of heat. In a refrigerator, heat is moved from inside the refrigerator to the room, cooling the food inside the refrigerator. Similarly, heat pumps move heat from outside a room to inside the room, warming it.
Combustion space heaters operate by burning a flammable fuel such as natural gas, kerosene, propane, or wood.
Convective space heaters
Many space heaters used in residential applications use convective heating. These can be divided into two categories: those with a fan to help spread the warmth, and those without a fan. Convective heaters are suitable for providing constant, diffuse heat in well-insulated rooms.
Convective with a fan
Some convective heaters use a fan to help distribute hot air around the room. This is one example of a fan heater. These heaters have heating elements made from either metal or ceramic, and the elements are in direct contact with the air in the room. This arrangement allows fan heaters to warm the room more quickly than those without fans.
Convective without a fan
Convective heaters without a fan are built so that the heating element is surrounded by either oil or water. These heaters warm the room more slowly because the oil or water must be heated first, and then the heat can reach the surrounding air. However, these heaters also produce longer-lasting heat after being turned-off because of the hot oil inside the heater.
The risk of fires and burns is sometimes less with oil-filled heaters than those with fans, but not always. Some fan-assisted heaters have a lower risk of fires and burns than some oil-filled heaters.
The main advantage of radiative heaters is that the infrared radiation they produce is absorbed directly by clothing and skin, without first heating the air in the space. This makes them suitable for warming people in poorly insulated rooms, or even outdoors. It also allows for greater distance between the people and heater.
Some of the earliest electric heaters were radiative, consisting of Nichrome heating wires held by ceramic or mica insulation at the focal point of a (usually) polished metal reflector. The cost was very low since nothing else, not even a switch, was needed. Later models included a wire guard preventing accidental contact with the heating wires or the hot ceramic.
However the metal reflectors needed to be fairly heavy gauge, and if the size was reduced then the metal housing would get too hot to be safe. In the mid-20th century, the cheapest heaters were radiative, but with the heating wires stretched relatively closely across a larger thin metal reflector separated from a thin metal housing. A small fan blew just enough air between the housing and the reflector to cool them; the main output to the room was the radiative heat and not the heated air. Having the heating wires stretched across a larger area meant that fewer expensive ceramic insulators were needed, and the small fan was cheaper than a larger or heavier housing.
Quartz heaters are radiative heaters which were more efficient, in the amount and directionality of heating, by using coiled heating wire inside unsealed quartz tubing. The wires could thus operate at a higher temperature than practical with ceramic-supported wires or be thinner. If the heating elements were at a higher temperature, then proportionally more energy was radiated compared to open-wire heaters.
Halogen heaters comprise tungsten filaments in sealed quartz envelopes, mounted in front of a metal reflector in a plastic case. They operate at a higher temperature than Nichrome wire heaters but not as high as incandescent light bulbs, radiating primarily in the infrared spectrum. They convert up to 86% of their input power to radiant energy, losing the remainder to conductive and convective heat. The halogen cycle reduces the darkening of the quartz envelope and lengthens the life of the filament.
Many of these space heaters, including those of oil-filled radiators and natural stone heaters, are plugged into an electric power source, most commonly a mains outlet. The power ratings of appliances are measured in kW, which allows an easy estimation of operation cost per hour, as energy is billed in kWh.
Fire, burns, and carbon monoxide poisoning are the main risks of space heaters. Approximately 25,000 fires are caused by space heaters in the United States in each year, resulting in about 300 deaths. In addition, approximately 6,000 hospital emergency department visits are caused in the US per year by space heaters, mostly from burns after touching the hot surface of a heater.
- Space heaters should either be plugged directly into the wall or into a heavy duty cord of 14-gauge wire or larger. Improper extension cords can cause fires.
- Plugs and cords should be periodically checked for cracks or damage, and replaced if damaged.
- Flammable materials such as curtains, furniture, and bedding should be kept at least 3 feet away from the heater.
- Turn-off the heater when the last adult leaves the room or goes to sleep. Children or pets should be kept 3 feet away from the heater.
- Place the heater on a flat, hard, and nonflammable surface.
- Avoid using heaters near flammable materials like paint or gasoline.
- Smoke alarms and carbon monoxide detectors should be installed nearby.
No one type of heater (i.e. oil-filled) is necessarily more safe than any other type. Risk of fire and burns can vary depending on the model and the manufacturer. However, lower surface temperatures generally reduce the risk of fire and burns. In addition, safety features have been added to some, but not all, space heaters. These safety switches will shut off the heater if a dangerous situation is detected:
- Tip-over sensors detect if the device is no longer upright (often found in the bases of halogen heaters).
- Thermal cut-out switches detect if the heating element becomes too hot.
- Airflow sensors detect if an object is blocking the exhaust of the heater.
Within the United States, Underwriters Laboratories maintains standards UL 1278 for portable electric space heaters, and UL 1042 for portable and fixed baseboard electric heaters. The General Services Administration used to maintain Specification W-H-193 for electric space heaters, but this was cancelled in 1995 in favor of the UL standards. Additional information on portable heater safety may be found at the Department of Energy Energy Efficiency website.
|Wikimedia Commons has media related to Space heaters.|
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