Types of Infrared Heater
The temperature output by a heater is dictated by the peak wavelength of thermal energy the emitter is designed to produce. All materials absorb heat differently according to the composition of the material itself plus its thickness. So the intended use of an emitter is a function of that peak wavelength plus the overall power being supplied to the emitter.
The three types of Infrared heater
There are 3 types of Infrared Heaters:
“Near Infrared”, “IRA”, “Short wave” or “Bright” Infrared heaters and “Heat Lamps” operate between 0.75 to 1.4 microns and emit temperatures of 1300°C and more plus a bright red visible light. Emitters are typically Quartz with a reflector to concentrate the heat in a particular direction. There are also gas-fired Near Infrared heaters which burn propane or natural gas through a venturi to heat a steel tube, which glows sufficiently hot to produce the near infrared.
Because of their high temperatures, near Infrared emitters are suitable for high intensity heat applications such as cooking and welding or thermoforming plastics. The heat is not suitable for Comfort heating applications. Near Infrared is deeply transmissive into Human and animal skin and is not effectively absorbed. To avoid the potential for damage, the skin has evolved to reflect large amounts of this wavelength which will not result in heating. Only infrared in the longer wavelengths assists with heat absorption in human and animal skin. Near infrared risks thermal burns to human and animal skin if a near infrared heater is placed too close to skin or if exposure is too long and ageing effects such as Bakers Arms and Glass-blowers face and eye damage can result from long term exposure. For Comfort heating, Medium and Longwave infrared should be considered, which don’t possess these harmful effects. Please see the attached article “Preferred wavelengths in Comfort Heating“.
“Medium Infrared”, “IRB” or “Medium Wave “ infrared heaters operate between 1.4 to 3 microns and emit temperatures of 500 – 800°C and produce a deep red light (like bar fires).
This type of radiation can be found naturally in smelting and glass-blowing processes and is the same range sought by heat-seeking missiles to detect the exhaust signatures of aircraft.
Quartz emitters consist of a heated wire coiled in a quartz glass tube, much like domestic “one bar” or “two bar” electric fires. The quartz tubes are supported in a metallic body. Applications at this wavelength include manufacturing processes such as curing of glues & coatings, welding of plastic parts, print toner curing, adding PVC backing to materials. Medium Infrared is also used for Industrial Drying.
Ceramic Emitters also emit in medium infrared (at 2 microns) but peak in the Far infrared (at 3 microns). This makes these sorts of emitter ideal for use in public and commercial “Space” heating applications because at the typical installation distances required in these situations they are energy-efficient and the emitted wavelength is safer to use than Tungsten/Halogen and the emitters are also much longer-lived.
“Far infrared”, “IRC”, “Long wave” or “Dark Radiators” operate in the wavelengths above 3 microns. Far Infrared elements emit much lower temperatures, typically around the 100°C mark and no visible light. Human and animal skin absorbs Far infrared specifically well, because of its 80% water composition, making Far Infrared a biologically significant heating wavelength for humans and animals.
Far Infrared heaters use a number of different elements, with popular ones being nickel or fecralloy wiring or more recently carbon fibre.
Because of their lower temperatures, applications of “Far Infrared” heating include Domestic, Commercial and Public “comfort” heating applications. It is also also used extensively in modern saunas.
General functional requirements to Infrared Type matrix
On the basis of the preceding, the following table shows approximately the considerations for matching the right type of infrared to the right requirement (for heating people).
Large open space to heat;Infrequent cycling of heater (for longevity);
Well out of reach of people (for safety);
No risk of prolonged exposure (eyes or skin).
Drying / Space Heating
Large open space to heat;Frequent cycling of heater possible;Closer proximity to people but must be out of reach.
Smaller spaces to heat;”Comfort” temperatures required;Within “touch” of people.
The effects of different types of Infrared on the Skin
It is important to show the different penetrative depths of the three types of IR into the skin versus their absorbancy rates as this helps underline their different uses, applications and precautions.
As the diagram to the left shows, “Far” Infrared (IR-C) is the least transmissive into the skin of the 3 types, but is actually the best absorbed by the blood and cells. This is quite sufficient for human “Comfort” heating, and avoids any possible health and safety issues with the use of Far Infrared.
Medium-wave Infrared or “IR-B” transmits slightly deeper into the lower epidermis, upper dermis layers but, like Far Infrared, does not transmit into the functional organs (sweat glands, nerves etc) carried by the skin. It is also well absorbed by the skin.
Near Infrared or “IR-A” is the most highly transmissive but least absorbed in the skin (in fact the skin has developed certain defenses that also naturally reflect up to 35% of Near Infrared). Near Infrared can transmit into the fatty subcutaneous layer, penetrating through the dermis and heating hair folllicles, sebacious (oil) glands, nerves and sweat glands. Because Near Infrared is high energy, this high transmission / low absorption rate is why it can damage the skin and why it is also used (under strict controls) for certain medical applications.