A space heater is a device used to heat a single, small area;central heating is used to heat many connected areas, such as the rooms of a house. Space heaters are powered by electricity or a burnable fuel, such as natural gas, propane, fuel oil, or wood pellets. Portable space heaters are usually electric, because a permanent exhaust is needed for heaters which burn fuel.
Space heaters are powered by electricity or the combustion of flammable fuel. Combustion space heaters burn flammable fuel, such as natural gas, kerosene, propane, or wood.
Electric space heaters fall into three main categories:
Many residential space heaters use convective heating. They can be divided into two categories: those with a fan (to distribute warmth), and those without a fan. Convective heaters provide constant, diffuse heat to well-insulated rooms.
Some convective heaters use a fan to help circulate warm air throughout a room. Their heating elements are metal or ceramic and are in direct contact with room air, allowing fan heaters to warm a room quickly.
In convective heaters without a fan, the heating element is surrounded by oil or water. These heaters warm a room more slowly, because the liquid must be heated before the heat can reach the surrounding air. They produce more heat after being turned off, however, because of the hot liquid inside the heater. The risk of fire (and burns) is sometimes less with oil-filled heaters than those with fans, but some fan-assisted heaters have a lower risk of fire (and burns) than other oil-filled heaters.
The main advantage of radiant heaters is that the infrared radiation they produce is absorbed directly by clothing and skin, without first heating the air in a space. This makes them suitable for warming people in poorly insulated rooms or outdoors, and allows more distance between people and the heater.
Some of the earliest electric heaters were radiant, 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 to prevent accidental contact with the heating wires or the hot ceramic.
The metal reflectors needed to be fairly thick, however; a thin metal housing would get too hot to be safe. Inexpensive mid-20th century heaters were radiant, 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, and the main output to the room was radiant heat (not heated air). Stretching the heating wires across a larger area required fewer (expensive) ceramic insulators, and a small fan was cheaper than a larger (or heavier) housing.
Quartz heaters are radiant heaters which are more efficient in the amount and direction of heat, with coiled heating wire inside unsealed quartz tubing. The wires could be thinner (or operate at a higher temperature) than ceramic-supported wires. If the heating elements are at a higher temperature, proportionally more energy is radiated than open-wire heaters.
Halogen heaters have 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 percent of their input power to radiant energy, losing the remainder to conductive and convective heat. The halogen cycle reduces darkening of the quartz envelope, extending filament life.
Many space heaters (including oil-filled radiators and natural stone heaters) are plugged into an electric power source, most commonly a two-prong - for older models - or three-prong outlet. Appliance power is measured in kilowatts (kW), which permits simple estimation of operating cost per hour (since electricity is billed in kilowatt hours, or kWh).
Fire, burns, and carbon monoxide poisoning are the main risks of space heaters. About 25,000 fires are caused by space heaters in the United States each year, resulting in about 300 deaths. Roughly 6,000 hospital emergency department visits annually in the US are caused by space heaters, mainly from burns.
No one type of heater is safer than any other type. The risk of fire and burns can vary, depending on model and manufacturer. However, lower surface temperatures generally reduce the risk of fire and burns. Safety features have been added to some space heaters. Safety switches will shut off the heater if a dangerous situation is detected:
In the United States, Underwriters Laboratories' UL 1278 (for portable electric space heaters) and UL 1042 standards (for portable and fixed baseboard electric heaters) certify heater safety. Although the General Services Administration had Specification W-H-193 for electric space heaters, it was replaced in 1995 by the UL standards. Additional information on portable-heater safety may be found at the Department of Energy Energy Efficiency website.