What do you mean "new" mortgage? Is it a refinancing without any of the proceeds being used to buy, build, or substantially improve the home that secures it?
If you used the new loan to pay off the old one, only the amount equal to the balance on the old debt qualifies for a deduction. If you paid off the old one outside of taking out the new debt, it would seem that none of the interest on the new one is deductible. However, if you provide more info about the new loan, like what it was used for, the answer could change
