space heater vs warmer

space heater and warmer both are nouns.

Word	Noun	Adjective	Verb	Adverb
space heater	Yes	No	No	No
warmer	Yes	No	No	No

As nouns, warmer is a hypernym of space heater; that is, warmer is a word with a broader meaning than space heater:

space heater: heater consisting of a self-contained (usually portable) unit to warm a room
warmer: device that heats water or supplies warmth to a room

Other hypernyms of space heater include heater.

space heater (noun)	warmer (noun)
heater consisting of a self-contained (usually portable) unit to warm a room	device that heats water or supplies warmth to a room