From school physics I recall the following means by which heat spreads out: conductance (particles bump against each other), radiation and the original heated mass moving (for example: sea currents).

Electromagnetic radiation heats things. For example: sunlight and infrared sauna.

Given these two hopefully correct recollections it would be tempting to say that all heat radiation is in fact electromagnetic radiation. Is this so and what is the mechanism behind such radiation appearing? Is the radiation concentrated around certain wave lengths (such as infrared) or distributed among different wave lengths in some other notable way?

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    $\begingroup$ If you mean thermal radiation, then yes, this is electromagnetic radiation. $\endgroup$ – HDE 226868 Mar 6 '16 at 18:55
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    $\begingroup$ yes: heat radiation is EM radiation - electromagnetic waves propagating through space - it is just light! see Is every electromagnetic radiation considered “light”? $\endgroup$ – AccidentalFourierTransform Mar 6 '16 at 18:55
  • $\begingroup$ Thermal radiation seems to be the correct term. My school education was not in English, so please pardon the faulty technical terminology. $\endgroup$ – Tommi Mar 6 '16 at 19:01
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    $\begingroup$ "Is the radiation concentrated around certain wave lengths (such as infrared) or distributed among different wave lengths in some other notable way?" Ideally the radiation is distributed in a way that is determined by the temperature of the radiating body. See Black Body radiation: en.wikipedia.org/wiki/Black-body_radiation $\endgroup$ – Lewis Miller Mar 6 '16 at 20:43

Electromagnetic (EM) Spectrum is an infinitely wide spectrum in both wavelength and frequency. This means a photon can generally have any positive wavelength or frequency. However, in such an infinite spectrum out eyes is capable of seeing "visible spectrum" meaning a wavelength interval of about $(380,740)$ nm out of a possible wavelength interval of $(0, \infty)$. Using different instrumentation we can see below 380 nm which is called ultraviolet (UV) or above 74 0nm which is called infrared (IR).

Thermal radiation or as you called it "heat" is a form of EM which is mostly in the (IR) wavelength. That's why we cannot see it by our eyes yet our skin can feel it. So, to give you a convincing answer, by radiation we mean ANY radiation in this infinite spectrum. When it is visible, we will see it as colors and when it is invisible and in the (IR) region we will call it heat.

But don't forget that ANY object which has temperature different than 0 Kelvin, would emit radiation in ANY wavelength depending on its temperature. If the temperature is too high, there will be extreme high-energy radiation such gamma rays and if it is too low there will be extreme low-energy radiation such as radio waves. This is why it is better to call it thermal rather than "heat".

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    $\begingroup$ To simplify the above answer, yes heat transfer through radiation is through EM waves. Thermal radiation is almost always in the Infrared region. But then again, the wavelength depends on the energy content of the radiation. $\endgroup$ – don_Gunner94 Mar 8 '16 at 5:43

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