SaunaTime® blog


The Heat Is On - An explanation of how far-infrared heat works. - By Craig Lahti

 "Do not Bodies and Light act mutually upon one another; that is to say, Bodies upon Light in emitting, reflecting, refracting and inflecting it, and Light upon Bodies for heating them, and putting their parts into a vibrating motion wherein heat consists?"

— Sir Isaac Newton

Opticks (1704), Book 3, Query 5, 133. 

Vitruvian Man

Over 300 years ago, Sir Isaac Newton discussed today's blog topic: how far-infrared heat works.  In recent years, as far-infrared saunas have grown in popularity, there has been a heated debate between traditional sauna and far-infrared sauna enthusiasts about which heat is better for a bather.  While this article will not identify a winner in the debate, it comes down to personal preference, the intent is to better educate both sides on the process by which a person is heated in an far-infrared sauna.

Before focusing on infrared heat exclusively, let us look at how a traditional sauna works, as many people will be surprised by the fact that a traditional sauna does heat through infrared heat, though the majority of the heat is achieved through conduction and convection.  Conduction is when the sauna heater elements are in direct contact with the rocks causing the rocks to be heated.  Convection occurs when gases and liquids are heated.  As the air and water (relative humidity, as well, as water is sprinkled on the rocks) are heated, the hotter air/water from the heater will displace the cooler air above the heater.  This displacement of cooler air by warmer air creates convection currents, which is why two levels of benches and cross-ventilation are important for traditional saunas to help keep bathers in the hottest temperatures of the room.  Infrared heat is emitted from the rocks, the sauna walls, and the other heated surfaces inside the room.  While this heat is infrared, the wavelength and intensity vary depending upon the surface temperature and the emissivity of the heated object, whereas the heat from far-infrared emitters in far-infrared saunas is more constant and often at a pre-engineered far-infrared wavelength.  When combined, convection, conduction, and radiation (infrared heat) produce the unique environment of the traditional sauna.

Convection air flow
The elements heating the rocks is conduction. The rocks and elements heating the air is convection (convection currents shown with red arrows). The hot walls and benches show radiant heat. 

To better understand far-infrared saunas, it is important to know infrared is naturally occurring and is part of the invisible portion of the electromagnetic spectrum.  On the spectrum, infrared is found between visible light and microwaves, with further subdivisions of near-infrared, mid-infrared, and far-infrared.  The following is a brief explanation of each subdivision.

                       IR light spectrum chart

Near-infrared has many uses.  According to George Melcher in his article Different Uses of Near Infrared Technology on, near infrared is used in fields from carpeting to medicine.  The deep penetrating waves can be used to analyze different materials used in recycled carpet as well as determining if a pharmaceutical pill has been manufactured properly.  For medical purposes, near infrared imaging of the brain may some day replace MRIs, as they are less expensive and can be used on a greater variety of patients.  NASA has also experimented with near-infrared technology for helping wounds heal faster.  Near infrared is also known as "reflected infrared" as it is the amount of near infrared that is reflected that is used for analysis of an object, whether it is carpet or the human brain.  One of the most common places to find near-infrared in daily use is the remote controls for our televisions and other electronic devices.

Mid-infrared moves into what is referred to as "thermal infrared".  Like near-infrared, mid-infrared has a wide range of uses.  For the military, it is used on heat seeking missiles to "lock" onto a heat signature.  Mid-Infrared lasers are also being used to detect enemy infrared countermeasures ( September 15, 2010 article Mid-IR emitters tipped for rapid market growth by Mike Hatcher).  For medical use, mid-infrared has been used in arthroscopic surgery and for less invasive diagnostics.  Like near-infrared, mid-infrared has great potential for advancement in medical technologies for diagnostics and treatment.  Because of its heat and deep penetration, mid-infrared is also used to cook and heat food.

Like mid-infrared, far-infrared is referred to as "thermal infrared"; however, far-infrared is closely aligned with the far-infrared waves the human body naturally emits, so the far-infrared is more readily absorbed by the body than the more intense energy of near or mid-infrared light.  The process by which far-infrared heat is created is similar to the heating of sauna rocks in a traditional sauna.  Before infrared energy (of any wavelength) is produced, the material from which the infrared energy is being emitted must be heated through conduction.  In a far-infrared sauna, the emitters, whether carbon, ceramic, or metal, must be heated before the far-infrared heat is emitted.  Though this process is very quick and the sauna can be enjoyed during this heat-up process, it is interesting to note that both traditional and far-infrared use conduction as the beginning heat source.  The far-infrared emitters in a sauna will continue to use conduction to produce radiant heat throughout the bathing experience.  Unlike the infrared heat in a traditional sauna, the emitters of a far-infrared sauna are engineered to keep the wavelengths in what is considered the "vital range" or 7 to 14 microns, with most being in the 8.4-9.4 range.

Whether your preference is a traditional or a far-infrared sauna, you now have a better understanding of the heating process of both.  Though near-infrared and mid-infrared are seldom discussed with regards to saunas, they are worth mentioning, as there are companies researching medical benefits, and possibly consumer health benefits, of these forms of infrared; however, far-infrared remains the most popular, and potentially beneficial form, of infrared heat therapy.

For more information on traditional, far-infrared, or a combination InfraSauna, contact your local dealer.  To read more about traditional or far-infrared products, request our brochure.  For more information on far-infrared saunas, take a virtual tour.
Infrared Heat


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Gloriana ( wrote:
This has made my day. I wish all poistngs were this good.