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B How do I measure the temperature of my infrared sauna?

  1. May 29, 2017 #1
    Sooooo..... I have a Far infrared (FIR) sauna. It has large flat 'carbon' panel heaters. They get warm to the touch and won't burn you if you touch them. My non contact infrared thermometer zapper says that they get to about 70 degrees C. They are meant to be producing lots of FIR.

    A regular mechanical dial thermometer at the top of the sauna (above the panels) shows that the temperature up there (after about 20 minutes of the sauna warming up) peaks at about 50 degrees C. I am assuming that while the direct radiant energy of the panels is FIR that is also striking the wood interiour of the sauna, heating it, and the wood in turn, is releasing / emitting IR, somewhere else on the spectrum.

    The FIR is 'said' to penetrate the body and warm you up producing an intense sweat even though the temperature of the room stays lower at only 50-60 deg C, as opposed to a conventional Finnish style sauna that heats up to 80-90 degrees with many people unable to handle the heat and sit comfortably for very long. I say yes it does make you sweat, whether this is because of the FIR, or because you are sitting in a box at 50 degrees, I can't say.I don't really see why the other parts of the IR spectrum would not penetrate you as well.

    My sauna wasn't 'feeling' hot enough for my liking so I retro-fitted a couple of conventional bar heaters (the old kind of glowing red, long quartz glass tube, with a tungsten filament inside). Now these make the sauna (or rather me!) feel a whole lot hotter, but they don't move the dial thermometer that much. They glow and are said to produce more near infra red (NIR). Obviously the bulbs are very hot (100's of degrees) and produce a lot of IR/heat, which decreases the further you get from them.

    Please, whats the right way to go about measuring the temperature at the position where I am sitting in the sauna with the NIR falling upon me?
    Last edited: May 29, 2017
  2. jcsd
  3. May 29, 2017 #2


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    The temperature of what?

    The air? The mechanical thermometer should measure that somewhat accurately, it gets more precise if you shield it against direct radiation.
    Your skin? That will be much lower, as your body cools the skin.
    The human skin, like everything else, reacts differently to different wavelengths.
    As rough trend, longer wavelengths reach deeper.
  4. May 29, 2017 #3


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    I think you are asking the wrong question...

    When you sit in a room that has a certain air temperature and humidity it produces a certain physiological response in the human body. The question is can that same response be reproduced when sitting in a room with a lower air temperature using direct IR heating?

    I don't know that it can. It would certainly be quite hard to avoid some parts of the body being in an IR "shadow".
  5. May 29, 2017 #4


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    Sorry to interject here, but you hit on a pet-peeve for me. There is no such thing as an infrared sauna. Without a means of tossing water onto a surface hot enough to turn it to steam, it is not a sauna. You may have a box in which gets warm inside and causes you to sweat, but that does not make it a sauna.
  6. May 30, 2017 #5
    mfb -Yes the mechanical thermometer does measure the air temperature, and does not react much to the increase in IR in the sauna. The thermometer is a round dial type with a shiney metallic exterior that probably reflects a lot of the IR. I don't want to measure air temperature. As you know IR passes through the air without heating it a lot and it tends to heat objects it reaches even through a vacuum.

    -OK but I would have thought that the shorter higher energy wavelengths reach deeper.
    Last edited: May 30, 2017
  7. May 30, 2017 #6
    Thank you CWatters, I think your right and I haven't asked the right question, which is why others might find it difficult to answer. I guess I am looking to equate the amount of energy that is falling on me in the IR sauna with the energy in a conventional sauna ? (lets put humidity to one side as you can have very dry conventional sauna as well)

    Is the heat/energy in a conventional sauna is mostly in the air? Certainly the air temperature is very hot and a mechanical thermometer is used to measure the temperature in these saunas accurately. Although I think that if the air is at 90 degrees C. Then most of the available surfaces will be quite hot as well and producing some IR in their own right?

    But if I sit in front of an IR heater then air temperature is no longer a good guide....is temperature a good guide?
  8. May 30, 2017 #7


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    Not on it's own.

    Air temperature, humidity, light (visible, IR and UV) and wind speed all effect our comfort level. I don't think you can use any one as a proxy for the overall experience. I suppose you could subject a large number of people to varying conditions and ask them to rate the "quality of the sauna experience". You might find there are several combinations that give similar answers. However as post #4 suggests not everyone will agree on what the best set of conditions is.

    Google seems to suggest that the air temperature in an infra red sauna should be around 110-130F...



    To measure the air temperature correctly you should probably shield the thermometer from direct radiation from the IR heater. Just as you shouldn't put the thermometer directly above a convection heater.
  9. May 30, 2017 #8


    Staff: Mentor

    For x-rays, but not for infrared.
  10. Jun 14, 2017 #9
    So conclusions...

    Temperature is something measured in substances (solids/liquids/gasses)?

    While I can measure the temperature in the IR sauna with a mechanical thermometer this will only show air temp.

    The temperature that I feel sitting in front of the NIR heaters in the sauna (which I find to be very hot!) is best categorised by subjective assessment. I can tolerate a 100 deg Celsius conventional sauna for say 10min. I can tolerate this IR sauna for about the same amount of time.
  11. Jun 14, 2017 #10


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    I think that just about sums it up. Humidity also effects your comfort level.
  12. May 16, 2018 #11
    Yes, they aren't lights but rather a carbon based thin panel that emits radiation in the IR spectrum. To get full IR impact you should be very close to them, but mine has a total of 14 heaters including the floor so not too hard to get close. For stretching the heat is all that matters. I got mine, one of those infra-red portable saunas, after reading Pollack's book and listening to Jack and was amazed at the energy (electrons) it gave me. If you live in a northern climate, I'm in Canada, it really shows you how much we miss the sun in the winter.
  13. May 17, 2018 #12
    Not necessarily: even void can have a temperature (cmbr, for example).
    You can also evaluate the "mean radiant temperature":
    What about using a "black globe thermometer"?

  14. May 18, 2018 #13
    This is tricky. Infrared can pass through some gases without heating them up much. Infrared on your skin in the same environment can warm you up quite a bit. Any thermometer will give you the air temperature. You can do a fun infrared project by making a "black box". It won't be rigorously accurate, bit it will give you an idea of what the infrared radiation is doing. Take a closed box (or a basketball) and paint the exterior flat black. Cut a small hole, insert a rod-type thermometer. Put it in the room, wait a bit. Compare the air temperature with the indicated temperature inside the "box". Note that this is just an approximation of the heating effect of the IR. Any flat black paint has some reflectivity. You can extend this by calculating the IR effect per irradiated unit area. Again, just fun, not terribly accurate.
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