stack up vs heap up

stack up and heap up both are verbs.

Word	Noun	Adjective	Verb	Adverb
stack up	No	No	Yes	No
heap up	No	No	Yes	No

As verbs, stack up and heap up are synonyms defined as:

Other synonyms of stack up include pile up.

stack up (verb)	heap up (verb)
arrange into piles or stacks	arrange into piles or stacks