heat vs red heat

heat and red heat both are nouns.

Word	Noun	Adjective	Verb	Adverb
heat	Yes	No	Yes	No
red heat	Yes	No	No	No

As nouns, red heat is a hyponym of heat; that is, red heat is a word with a more specific, narrower meaning than heat:

Other hyponyms of heat include calefaction, incalescence, fieriness, torridity, warmness, warmth, white heat.

heat (noun)	red heat (noun)
utility to warm a building	the heat or the color of fire
the presence of heat
the trait of being intensely emotional
the sensation caused by heat energy
a preliminary race in which the winner advances to a more important race
a form of energy that is transferred by a difference in temperature
applies to nonhuman mammals: a state or period of heightened sexual arousal and activity

heat (verb)	red heat (verb)
gain heat or get hot
make hot or hotter
arouse or excite feelings and passions
provide with heat