heat vs hot up

heat is a noun but hot up is not a noun.

Word	Noun	Adjective	Verb	Adverb
heat	Yes	No	Yes	No
hot up	No	No	Yes	No

As verbs, heat and hot up are synonyms defined as:

Other synonyms of heat include heat up.

heat (noun)	hot up (noun)
utility to warm a building
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)	hot up (verb)
gain heat or get hot	make more powerful
make hot or hotter	make more intense
arouse or excite feelings and passions	gain heat or get hot
provide with heat