Air Temperature and Infrared Saunas: When 130°F does not equal 130°F
Let’s talk about air temperature in an infrared sauna. It is not an intuitive concept that an infrared sauna can heat your body better and faster, at lower air temperatures, than can a traditional sauna. We tend to think that numbers are fairly straightforward, and that higher temps mean more heat. But this is not exactly the case.
Temperature of Things Around Us vs Heat Transfer To Us: An Important and Overlooked Distinction
Temperature is a measure of how much heat a substance (the air) contains. However, it does not measure how much heat is being transferred to your body, which is the only thing that matters to you. If the air is 500°F, but none of that heat is being transferred into your body, you won’t even feel warm.
Most people know that air temperature and water temperature are not the same. Air at 111°F can be quite pleasant and relaxing, depending on the circumstances, while water at 111°F is hot enough to cause thermal skin burns1.
This is because water is a much better heat conductor than air, i.e. it transfers much more heat to us much faster than does air. In fact, air is one of the worst heat conductors, which is why it makes the best insulator. The most effective insulation materials depend on their ability to trap air.
Heat Transfer
When using a sauna, the goal is to raise your core body temperature. I would love to go into a longer discussion about heat shock proteins and the amazing benefits, and how to best activate them, but I will stay on track. The goal is to raise your core body temperature quickly, as studies show that the rate may be as important as the degree of rise in activating heat shock proteins. Again, the only thing that matters is how much heat is being transferred to your body. Let’s look at the ways this can happen.
The three methods of heat transfer:
Conduction– a hot object comes into contact with another object. You touch a stove, your hand gets hot. That is conduction.
Convection– heat transfer through air or water. The air is heated, the air moves over to you, and the hot air then transfers heat to you. This is how traditional saunas work.
Radiation– I am not talking about ionizing radiation like X-rays or gamma rays. Ionizing radiation is damaging and should be avoided. Infrared is on the opposite end of the visual spectrum, past red, as the wavelengths get longer and longer. The word “radiation” applies to radiant heat transfer by light waves, primarily by the long, beneficial wavelengths of far infrared.
In a traditional sauna, hot air is the only source of heat, and heat is transferred to you by convection. This is an inefficient method of heating (remember, air is an insulator). They use a lot of power and are very slow to heat up. So, infrared saunas were invented. Infrared saunas transfer heat to us through radiant heat, a much faster and more efficient method of heat transfer that is not measured by air temperature. High Tech Health saunas do have a thermometer, and the air does get hot (maximum air temp 158°F). However, this is not the primary method of heat transfer.
A Black Plate Experiment: Heat Transfer and Temperature rise, With and Without Infrared
Heat transfer by convection can only heat an object to the temperature of the air. When it reaches the temperature of the air, it is at equilibrium, and there is nowhere for more heat to come from. Radiant heat does not depend on the temperature of the air or another object, and can heat an object far past the air temperature.
Let’s talk about a black plate (because it absorbs infrared well) lying in the shade, compared to the same plate lying in direct sun, on a mild day of 68°F. In the shade, the plate will equalize with the air, and reach 68°F. In the sun, right next to the shady spot at the same air temperature, it can heat up to 131°F.
This was a complicated calculation done by the smart people at UCSD, based on the amount of the solar energy at the earth’s surface, the absorption of infrared by the plate, and the amount of heat that the plate can dissipate through air flow2. I think anyone who has walked barefoot across pavement or leaned on a hot car sitting in the sun can relate.
In the shade, the air temperature would have to be 131°F to heat the plate to the same temperature. In this example, the infrared adds an amount of heat transferred equivalent to an additional 63°F in air temperature.
Infrared Saunas Raise Core Body Temperature
Both our own research and published studies show infrared saunas raise core body temperature. Studies have been published showing that infrared saunas effectively raise core body temperature at air temperatures of 122°F3 to 135°F4.
We are referencing these published studies to bolster our own data, but far more significant are the thousands of data points that we ourselves measured in a company wide multi-year long experiment. All of us own and use a High Tech Health sauna, and we all participated in taking frequent core temperature measurements while using our saunas, with a starting air temperature of 100°F.
We all consistently saw a rise in core body temperature by 10 minutes. On average, the rise in core body temperature by 20 to 30 minutes significantly exceeded numbers determined to activate heat shock protein production. This data was used as a part of the research to design our new Transcend® Smart Sauna, which predicts your core body temperature during a sauna session.
High Tech Health and our Transcend Smart Sauna: A smarter sauna from a smarter company
Our Transcend® Smart Sauna is a topic for another article, but a brief summary is: Based on your rise in core body temp and your pattern of use, it can predict your percentage of heat acclimation (Sauna Fitness™), and guide you to getting to 100%. Heat acclimation is a state where your heat shock proteins are elevated at baseline, and is a marker of all the health benefits that come with regular sauna use. It is exciting technology that we think will change the infrared sauna industry.
High Tech Health is not your typical infrared sauna company. Our team of sauna experts all hold advanced science degrees and we love talking about the science of infrared saunas. When you work with us, you gain access to unparalleled expertise that goes beyond just selling products. When other companies don’t have the answers, we do.
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