An infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the infrared radiation ranges from 780 nm to 1 mm. The relationship between temperature and wavelength is expressed by the Stefan-Boltzmann Law. No contact or medium between the two bodies is needed for the energy transfer. A rough classification of infrared heaters is connected to wavelength bands of major emission of the energy: short wave or near infrared for the range from 780 nm to 1400 nm, these emitters are also named bright because still some visible light with glare is emitted; medium infrared for the range between 1400 nm and 3000 nm; far infrared or dark emitters for everything above 3000 nm.

Elements of infrared heater

For practical purposes, most infrared heaters are constructed by either using the emission of a flame (usually soot or a heated matrix) or an electrically heated filament as the emitting body. If an electrically operated infrared heater (infrared lamp) is used, the filament is usually protected by a heat-resistant quartz glass tube. Depending on the filament temperature, a filling of the quartz tube with inert gas (e.g., halogen) may be required to prevent filament degradation. These emitters use the same materials and principle as a light bulb.

The most common filament material used for electrical infrared heaters is tungsten wire, which is coiled to provide more surface area. Low temperature alternatives for tungsten are carbon , or alloys of iron, chromium and aluminum (brand name ‘kanthal’). While carbon filaments are more fickle to produce, they heat up much quicker than a comparable medium-wave heater based on a FeCrAl filament.

Industrial infrared heaters sometimes use a gold coating on the quartz tube that reflects the infrared radiation and directs it towards the product to be heated. Consequently the infrared radiation impinging on the product is virtually doubled. Gold is used because of its oxidation resistance and very high IR reflectivity of approximately 95 %