As long as the HELOC was taken out within 90 days of completion of construction, you can consider both the HELOC and the mortgage as fully deductible acquisition debt.
In Turbotax, enter both loans separately, you will be asked for each loan, if it was used to buy, build or substantially improve your home. Say yes. (Unless part of the HELOC was used for other things, then it is only partly deductible and you will have to do a calculation.)
