heating vs gas heat

heating and gas heat both are nouns.

Word	Noun	Adjective	Verb	Adverb
heating	Yes	No	No	No
gas heat	Yes	No	No	No

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

Other hyponyms of heating include central heating, panel heating, steam heat, steam heating.

heating (noun)	gas heat (noun)
utility to warm a building	heating system that burns natural gas
the process of becoming warmer; a rising temperature