Hi Wall
Pay off the new home loan first including reducing the amount you need to borrow if neccessary. The other loan which will become a rental will have 75% of the interest deductible against the rental income. Before you decide to rent the other property you need to consider what is the gross rent and the net rent. There are alot of deductions that need to be made from the monthly rent payable (Tax, PRTB, Sinking Fund, Etc) If this leaves you in a position of affordability then it could make sense and hopefully the property may increase in value over time (you need also consider what your first property was bought for in terms of capital gains tax if you sell it in the future) but to answer your question re lump sum make any lump sum you have payable to the new home loan as there is no relief on that loan. Hope this helps Padraic