steam heat vs heating plant

steam heat and heating plant both are nouns.

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

As nouns, heating plant is a hypernym of steam heat; that is, heating plant 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 plant: utility to warm a building

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

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