there are tracing rules. if you follow the Regs 1.163-8T and 10T. then it depends what you use the HELOC for. put it into a brokerage account and it's investment interest (schedule a) and therefore the deduction would be limited to investment income. use it to buy a recreational boat (not for profit) it isn't deductible at all.
you might even want to read this about HELOC
https://content.govdelivery.com/accounts/USIRS/bulletins/1dca891
(IR-2018-32)
especially example 1
tax simplification at its finest
