steam heat vs heating system

steam heat and heating system both are nouns.

Word	Noun	Adjective	Verb	Adverb
steam heat	Yes	No	No	No
heating system	Yes	No	No	No

As nouns, heating system is a hypernym of steam heat; that is, heating system is a word with a broader meaning than steam heat:

steam heat: a heating system in which steam is generated in boilers and piped to radiators
heating system: utility to warm a building

Other hypernyms of steam heat include heat, heating, heating plant.

steam heat (noun)	heating system (noun)
a heating system in which steam is generated in boilers and piped to radiators	utility to warm a building