Heaters are surely the most important part of every far infrared sauna. They produce heat, which is why this wooden box is known as a sauna. Most of the heat they provide comes in the form of infrared (or thermal) radiation, which is why these types of heaters are called infrared (far infrared) or radiant heaters. The promotional efforts of most brands focus on the heaters used in a sauna, trying to make the buyer believe that they have the best heater.
The arguments used are wavelengths, heater temperatures, heater surface area, heater material, heater positions, heater shape, and heater duty cycle. The promises of the best wavelength and best heat distribution (both in time and space) are heard everywhere. In addition to that, companies do not hesitate to criticize their competitors’ heaters.
This high noise level leads to the situation that it is very difficult for the customer to make a decision about which heater he wants in his sauna. The fact that the heaters look like the most sophisticated part of the sauna (as opposed to the wooden enclosure, lighting, ventilation, and other things) adds further confusion. And things seem more complicated because far infrared sauna companies often use words as well as scientific terms when describing their heaters.
Actually, understanding how the heater works is not complicated at all. Much of the noise around far infrared heaters is over-emphasized. This is my opinion and I am going to make two statements about infrared heaters and support them with facts.
Fact 1. The difference between the infrared rays generated by different types of heaters is not that important; in fact, it is less important than other aspects of heaters.
Fact 2. The range of wavelengths emitted by a heater depends only on its temperature (see thermal radiation). Radiant heaters do not contain any technology other than heating the heater material with a metal coil embedded in it. Current passes through the metal coil, heats it up (similar to a common light bulb), and then heat is transferred from the coil to the body of the heater.
Fact 3. The temperature of the heaters used in a far infrared sauna varies between approx. 60 C (140 F) (some charcoal heaters, but even these heaters generally run at higher temperatures) to 760 C (1400 F) (aluminum or Incoloy heaters).
Fact 4. The maximum wavelength of a heater at 60 C (140 F) is 8.7 microns (Wien’s law) and the maximum wavelength of a heater at 760 C (1400 F) is 2.8 microns. Both are in the mid-far infrared part of the spectrum. And for each heater, the emitted wavelengths are fairly evenly distributed around their maximum wavelength (see Planck’s radiation law illustrated in this image).
Fact 5. Infrared only warms our bodies. Transfers energy from heaters to the surface of the human body. That’s all. All the effects that the infrared sauna has are derived from this fact. I have not seen any reference to research or other sources to claim that certain infrared wavelengths are more beneficial to humans than others.
Fact 6. Walls at room temperature 20 C (68 F) emit far-infrared with a 9.8-micron peak. The human being, standing in a room, receives about 400 watts of infrared heat from the walls, ceiling, and floor. So the key property of a far infrared sauna is heat, not far-infrared.
Fact 7. The most important thing in an infrared sauna is how the heat is evenly distributed throughout the human body and how this heat changes during the sauna session. Any heater will do if it provides a good distribution of heat in time and space.
Fact 8. The situation where one part of the body becomes less hot than the other (e.g. legs and torso) is unpleasant and therefore unacceptable. It can even be dangerous since our body’s thermoregulatory systems can get confused and not react properly to overheating.
Fact 9. To keep the sauna temperature at a constant level, sauna companies use different solutions: turning the heaters on and off during the sauna session, reducing the power of the heater as the temperature increases, or maintaining the power of the constant heater but to increase ventilation. The different It’s methods lead to different sensations and different bodily reactions when taking a sauna.
Fact 10. The distribution of heat and the change in heat intensity with time is largely in a field of personal preference. One person may dislike his burning head, others may not. Some people may like the level of heat that rises and falls gradually, others may like the constant heat plus ventilation. There is no one-size-fits-all solution.