I need to take this a step farther.
For January, you can deduct the interest on the original mortgage but not the HELOC. For Feb-December, you deduct a percentage of the interest equal to the percentage of acquisition debt. When first refinanced, the acquisition debt is $100,000/$115,000 = 86.9%. However, you can consider that you pay off the equity debt first, so by December, your total loan balance might be $112,000, which is 89.3% acquisition debt. You can average those two values to get the overall deduction for 2020 of 88.1%. Turbotax should do this calculation for you but that's how it's supposed to work.
