Question : what is the unit of heat do they possess. (photons)

Whatever unit of energy you want to use. Joules, ergs, electron-volts, etc.

Whatever unit of energy you want to use. Joules, ergs, electron-volts, etc.

does it depend of the frequency of the wave ? and the charge ( Watts).

The energy of a photon is directly proportional to its frequency (e=hf). The range of frequencies from a black body is:

https://en.wikipedia.org/wiki/Black-body_radiation#Spectrum

 

(Watts is a unit of power not charge)

does it depend of the frequency of the wave ? and the charge ( Watts).

No. It's common to use a unit appropriate to the scale (e.g. Joules vs eV is large vs small) but energy is energy. You can do a conversion from one unit system to another.

 

EM waves do not have a charge.

 

A watt is a unit of power, which is a rate of energy transfer (watt = joule/second)