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{{Short description|Device designed to create radiative heat}}
{{Lead too short|date=September 2023}}
[[File:Carbon heater.jpg|thumb|upright|A household infrared electric heater]]
An '''infrared heater''' or '''heat lamp''' is a heating appliance containing a high-temperature emitter that transfers energy to a cooler object through electromagnetic radiation. Depending on the temperature of the emitter, the wavelength of the peak of the [[infrared radiation]] ranges from {{val|750|ul=nm}} to 1 mm. No contact or medium between the emitter and cool object is needed for the energy transfer. Infrared heaters can be operated in [[vacuum]] or atmosphere.
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===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<ref>{{Cite web |last=Williams |first=Dawn |date=2017-11-02 |title=Where Should I Place My Infrared Heater? |url=https://www.infraredheatersdirect.co.uk/news/where-should-i-place-my-infrared-heater/ |access-date=2022-09-18 |website=Advice Centre |language=en-GB |archive-date=2020-10-31 |archive-url=https://web.archive.org/web/20201031044229/https://www.infraredheatersdirect.co.uk/news/where-should-i-place-my-infrared-heater/ |url-status=dead }}</ref> or integrated in floors.<ref>{{Cite web |title=Infrared Underfloor Heating |url=https://www.eco-world-northeast.com/product-range/infrared-underfloor-heating/ |access-date=2022-09-18 |website=Eco World Northeast Limited |language=en-GB}}</ref> 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.<ref>{{Cite web |title=Infrared Panels NZ |url=https://infraredpanels.co.nz/the-green-technology-behind-far-infrared-heating |access-date=2022-09-18 |website=Infrared Panels NZ |language=en}}</ref> 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.<ref>{{
===Quartz heat lamps===
[[File:Clear Quartz Element Example.jpg|thumb|upright=0.26|Clear quartz element]]
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 {{
Quartz infrared heating elements<ref>{{Cite web |title=Quartz Heating and How it Works {{!}} Tansun |url=https://www.tansun.com/gb_en/technical/how-quartz-heating-works.html |access-date=2024-05-08 |website=www.tansun.com}}</ref> 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 {{Convert|2500|K|°C °F}}, producing more shorter-wavelength radiation than open wire-coil sources. Developed in the 1950s at [[General Electric]], these lamps produce about {{Convert|100|W/in|W/mm|0|abbr=out}} and can be combined to radiate {{Convert|500|W/ft2|W/m2|abbr=out}}.{{Citation needed|date=September 2021}} To achieve even higher power densities, [[halogen lamp]]s 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 {{Convert|28|kW/ft2|kW/m2|abbr=on}}.<ref>Raymond Kane, Heinz Sell ''Revolution in lamps: a chronicle of 50 years of progress (2nd ed.)'', The Fairmont Press, Inc. 2001 {{ISBN|0-88173-378-4}} chapter 3</ref> In 2000, General Electric launched the first quartz waterproof lamp alongside British infrared heating manufacturer Tansun.<ref>{{Cite web |title=History of Tansun {{!}} Infrared Space Heater Manufacturer |url=https://www.tansun.com/gb_en/about-us/about-history.html |access-date=2024-05-08 |website=www.tansun.com}}</ref>
Most common designs consist of either a satin [[Fused quartz|milky-white quartz glass]] tube or clear [[quartz]] with an electrically resistant element, usually a [[Tungsten filament#Filament|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.
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* 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
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.)
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Electrically heated infrared heaters radiate up to 86% of their input as radiant energy.<ref>''2008 ASHRAE Handbook – Heating, Ventilating, and Air-Conditioning Systems and Equipment (I-P Edition)'', American Society of. Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2008, Electronic {{ISBN|978-1-60119-795-5}}, table 2 page 15.3</ref> Nearly all the electrical energy input is converted into infrared [[radiative heat transfer|radiant heat]] in the filament and directed onto the target by reflectors. Some heat energy is removed from the heating element by [[Conduction (heat)|conduction]] or [[Convection (heat transfer)|convection]], which may be no loss at all for some designs where all of the electrical energy is desired in the heated space, or may be considered a loss, in situations where only the radiative heat transfer is desired or productive.
For practical applications, the efficiency of the infrared heater depends on matching the emitted wavelength and the absorption spectrum of the material to be heated. For example, the absorption spectrum for water has its peak at around {{val|3|u=μm}}. This means that emission from medium-wave or carbon infrared heaters is much better absorbed by water and water-based coatings than NIR or short-wave infrared radiation. The same is true for many [[plastics]] like PVC or polyethylene. Their peak absorption is around {{val|3.5|u=μm}}. On the other hand, some metals absorb only in the short-wave range and show a strong reflectivity in the medium and far infrared. This makes a careful selection of the right infrared heater type important for [[energy conversion efficiency|energy efficiency]] in the heating process.<ref>{{
Ceramic elements operate in the temperature of {{convert|300|to|700|°C|°F|-1}} producing infrared wavelengths in the 2 to {{val|10|u=μm}} range. Most plastics and many other materials absorb infrared best in this range, which makes the ceramic heater most suited for this task.<ref>{{Cite web|date=2017-06-25|title=36 Mind Blowing Facts about Infrared Radiation (IR Rays)|url=https://www.infrared-light-therapy.com/infrared-radiation/|access-date=2021-01-24|website=InfraRed Light Therapy|language=en}}</ref>{{citation needed|date=April 2011}}
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