Metal wire element

Metal wire heating elements first appeared in the 1920s. These elements consist of wire made from chromel. Chromel is made from nickel and chrome and it is also known as nichrome. This wire was then coiled into a spiral and wrapped around a ceramic body. When heated to high temperatures it forms a protective layer of chromium oxide which protects the wire from burning and corrosion, and causes the element to glow.^[5]

Heat lamps

A heat lamp is an incandescent light bulb that is used for the principal purpose of creating heat. The spectrum of black-body radiation emitted by the lamp is shifted to produce more infrared light. Many heat lamps include a red filter to minimize the amount of visible light emitted. Heat lamps often include an internal reflector.

Heat lamps are commonly used in shower and bathrooms to warm bathers and in food-preparation areas of restaurants to keep food warm before serving. They are also commonly used for animal husbandry. Lights used for poultry are often called brooding lamps. Aside from young birds, other types of animals which can benefit from heat lamps include reptiles, amphibians, insects, arachnids, and the young of some mammals.

The sockets used for heat lamps are usually ceramic because plastic sockets can melt or burn when exposed to the large amount of waste heat produced by the lamps, especially when operated in the "base up" position. The shroud or hood of the lamp is generally metal. There may be a wire guard over the front of the shroud, to prevent touching the hot surface of the bulb.

Ordinary household white incandescent bulbs can also be used as heat lamps, but red and blue bulbs are sold for use in brood lamps and reptile lamps. 250 watt heat lamps are commonly packaged in the "R40" (5" reflector lamp) form factor with an intermediate screw base.

Heat lamps can be used as a medical treatment to provide dry heat when other treatments are ineffective or impractical.^[6]

Ceramic infrared heat systems

Ceramic infrared heating elements are used in a diverse range of industrial processes where long wave infrared radiation is required. Their useful wavelength range is 2–10 μm. They are often used in the area of animal/pet healthcare too. The ceramic infrared heaters (emitters) are manufactured with three basic emitter faces: trough (concave), flat, and bulb or Edison screw element for normal installation via an E27 ceramic lamp holder.

Far-infrared

This heating technology is used in some expensive infrared saunas. It is also found in energy efficient space heaters. They are usually fairly big flat panels that are placed on walls, ceilings^[7] or integrated in floors.^[8] These heaters emit long wave infrared radiation using low watt density ceramic emitters based on carbon fibre technology. More efficient designs use carbon crystals, a combination of carbon fibre, integrated with nanotechnology, transforming carbon into nanometer form.^[9] Because the heating elements are at a relatively low temperature, far-infrared heaters do not give emissions and smell from dust, dirt, formaldehyde, toxic fumes from paint-coating, etc.^{[citation needed]} This has made this type of space heating very popular among people with severe allergies and multiple chemical sensitivity in Europe.^{[citation needed]} Because far infrared technology does not heat the air of the room directly, it is important to maximize the exposure of available surfaces which then re-emit the warmth to provide an even all round ambient warmth. This is known as radiant heating.^{[citation needed]}

Quartz heat lamps

Halogen lamps are incandescent lamps filled with highly pressurized inert gas combined with a small amount of halogen gas (bromine or iodine); this lengthens the life of the filament (see Halogen lamp#Halogen cycle). This leads to a much longer life of halogen lamps than other incandescent lamps. Due to the high pressure and temperature halogen lamps produce, they are relatively small and made out of quartz glass because it has a higher melting point than standard glass. Common uses for halogen lamps are table top heaters.^[10][11]

Quartz infrared heating elements emit medium wave infrared energy and are particularly effective in systems where rapid heater response is required. Tubular infrared lamps in quartz bulbs produce infrared radiation in wavelengths of 1.5–8 μm. The enclosed filament operates at around 2,500 K (2,230 °C; 4,040 °F), producing more shorter-wavelength radiation than open wire-coil sources. Developed in the 1950s at General Electric, these lamps produce about 100 watts per inch (4 W/mm) and can be combined to radiate 500 watts per square foot (5,400 W/m²).^{[citation needed]} To achieve even higher power densities, halogen lamps were used. Quartz infrared lamps are used in highly polished reflectors to direct radiation in a uniform and concentrated pattern.

Quartz heat lamps are used in food processing, chemical processing, paint drying, and thawing of frozen materials. They can also be used for comfort heating in cold areas, in incubators, and in other applications for heating, drying, and baking. During development of space re-entry vehicles, banks of quartz infrared lamps were used to test heat shield materials at power densities as high as 28 kW/sq ft (300 kW/m²).^[12]

Most common designs consist of either a satin milky-white quartz glass tube or clear quartz with an electrically resistant element, usually a tungsten wire, or a thin coil of iron-chromium-aluminum alloy. The atmospheric air is removed and filled with inert gases such as nitrogen and argon then sealed. In quartz halogen lamps, a small amount of halogen gas is added to prolong the heater's operational life.

The majority of the radiant energy released at operational temperatures is transmitted through the thin quartz tube but some of that energy is absorbed by the silica quartz glass tube causing the temperature of the tube wall to increase, this causes the silicon-oxygen bond to radiate far infrared rays.^{[citation needed]} Quartz glass heating elements were originally designed for lighting applications, but when a lamp is at full power less than 5% of the emitted energy is in the visible spectrum.^[13]

Quartz tungsten

Quartz tungsten infrared heaters emit medium wave energy reaching operating temperatures of up to 1,500 °C (2,730 °F) (medium wave) and 2,600 °C (4,710 °F) (short wave). They reach operating temperature within seconds. Peak wavelength emissions of approximately 1.6 μm (medium wave infrared) and 1 μm (short wave infrared).

Carbon heater

Carbon heaters use a carbon fiber heating element capable of producing long, medium and short wave far infrared heat. They need to be accurately specified for the spaces to be heated.^{[citation needed]}

Gas-fired

There are two basic types of infrared radiant heaters.

• Luminous or high intensity
• Radiant tube heaters

Radiant tube gas-fired heaters used for industrial and commercial building space heating burn natural gas or propane to heat a steel emitter tube. Gas passing through a control valve flows through a cup burner or a venturi. The combustion product gases heat the emitter tube. As the tube heats, radiant energy from the tube strikes floors and other objects in the area, warming them. This form of heating maintains warmth even when a large volume of cold air is suddenly introduced, such as in maintenance garages. They cannot however, combat a cold draught.

The efficiency of an infrared heater is a rating of the total energy consumed by the heater compared to the amount of infrared energy generated. While there will always be some amount of convective heat generated through the process, any introduction of air motion across the heater will reduce its infrared conversion efficiency. With new untarnished reflectors, radiant tubes have a downward radiant efficiency of about 60%. (The other 40% comprises unrecoverable upwards radiant and convective losses, and flue losses.)