可以抵別外那個房子的租金。

based on interest tracing rule, tax status of the interest of HELOC depends on its usage.

If the HELOC is used for improve primary residence,  then the interest is part of the primary residence mortage deduction.

If the HELOC is used to acquire a rental property, then interest is part of expense of that rental property, and deducitble against its rental income. 

If the HELOC is used for vacation, the interest is not deductible.