Electric Resistance Heat

When your feet get cold but you don't want to turn up the heat throughout the building, you might want to use an electric resistance space heater. These common, low-cost, and easy-to-install small heaters offer individual thermostatic control and don't waste heat in unoccupied rooms. However, they use expensive electricity as their fuel, so their use should be limited to spot-heating a small area for a limited time in an otherwise cool building.

The first electric room heater was patented in 1892 by the British inventors R. E. Compton and J. H. Dowsing, who had attached several turns of high-resistance wire around a flat rectangular plate of cast iron. The glowing white-orange wire was set at the center of a metallic reflector, which concentrated the heat into a beam. The success of their heater depended upon homes being wired for electricity, which was becoming more popular thanks to Edison's invention of the electric light.

In 1906, Illinois inventor Albert Marsh modified the original design with a nickel and chrome radiating element, producing white-hot temperatures without melting. In 1912, the British heater replaced the heavy cast-iron plate with a lightweight fireproof clay one, creating the first really efficient portable electric heater.

An electrical resistance system works like a toaster: wires heat up when you turn it on. Electric resistance heating takes advantage of the way electrical energy is converted to heat when it has difficulty passing along a conductor. Most of the time such a system consists of baseboard units or small, wall-mounted heaters, both of which contain the hot wires. The heaters are inexpensive and clean, and don't have to be vented. No space is used for chimneys or fuel storage.

Electric heating units designed for residential use combine a radiant heating element with a fan and a light in a ceiling-mounted unit. Some units include a nightlight as well. Bulb heaters provide silent, instant warmth using 250W R-40 IR heat lamps. Bulb heaters are available vented and unvented, and recessed or surface mounted. Auxiliary heaters are available for mounting in or on walls, and in kickspaces below cabinets.

Electrical resistance heating units (Fig. 24-10) are compact and versatile, but lack humidity and air quality controls. Electric resistance heaters use high-grade electrical energy for the low-grade task of heating. These heaters have hot surfaces, and their location must be carefully chosen in relation to furniture, drapery, and traffic patterns.

The elements of an electric resistance heating system can be housed in baseboard convection units around the perimeter of a room. Resistance coils heat room air as it circulates through the units by convection. Electric unit heaters use a fan to draw in room air and pass it over resistance-heating coils, then blow it back into the room.

Units are available that can be wall- or ceiling-mounted for bathrooms and other spaces where the floor might be wet but where quick heat for a limited time in an enclosed space is needed. Infrared heat lamps are also installed in bathroom ceilings for this purpose.

Toe space unit heaters are designed to be installed in the low space under kitchen and bathroom cabinets. Wall unit heaters are available in surface mounted or recessed styles for use in bathrooms, kitchens, and other small rooms. Fully recessed floor unit heaters are typically used where glazing comes to the floor, as at a glass sliding door or large window. Industrial unit heaters are housed in metal cabinets with directional outlets, and are designed to be suspended from the ceiling or roof structure. Quartz heaters have resistance heating ele ments sealed in quartz-glass tubes that produce IR radiation in front of a reflective background.

Small high-temperature IR heat sources with focusing reflectors can be installed in locations where they don't cast IR radiation shadows, such as overhead. They are useful where high air temperatures can't be maintained, as in large industrial buildings or outdoors. IR heaters are often used at loading docks, grandstands, public waiting areas, garages, and hangers. They will melt snow over limited areas.

Small IR heaters radiate a lot of heat instantly from a small area, and beam the heat where needed. High-temperature IR heaters may be electrical, gas-fired, or oil-fired. Venting is required for oil and sometimes for gas. The temperatures in the units can be greater than 260°C (500°F). Their radiant heat feels pleasant on bare skin, making these devices desirable for swimming pools, shower rooms, and bathrooms.

Portable electric resistance heaters heat a small area in their immediate vicinity without heating an entire building. However, their use as a substitute for building heating inevitably leads to deaths each year, when they are left running all night and come in contact with bedding or drapery, or where they are connected to unsafe building wiring.

There are several types of portable electric resistance heaters available today. Quartz heaters use electricity to quietly heat the floors and furniture within about 15 feet. You only feel their warmth if you stand nearby. Electrical forced air heaters are best used in a room that can be closed off. Electrical forced air heaters blow warm air and circulate it throughout a room. Ceramic forced air heaters use a ceramic heating element that is safer than other electric space heaters. Electricity heats the oil

Toespace unit heaters use a fan to blow air into room from below cabinets.

Recessed floor unit heaters with fans are located below windows.

Recessed floor unit heaters with fans are located below windows.

Toespace unit heaters use a fan to blow air into room from below cabinets.

Figure 24-10 Electric resistance heating.

Recessed or surface-mounted wall unit heaters are used in bathrooms, kitchens, and small rooms.

Electric resistance elements baseboard convector ¿—^

Electric resistance elements baseboard convector ¿—^

Figure 24-10 Electric resistance heating.

inside oil-filled heaters to heat a room or temporarily replace a main heat source.

Electric resistance heating elements can also be exposed to the airstream in a furnace or mounted inside ductwork in forced air heating systems. Sometimes they are used to provide heat for a boiler in a hydronic heating system.

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