Is heat radiation an instance of electromagnetic radiation? 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?
 A: 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".
