The key differences are the rates applicable, the term of the debt and the total interest paid. On a very quick and dirty calculation, the interest payable over the remaining term of the car loan is about 1.6k and about 1.9k on the credit union loan. So in terms of consolidating, makes sense to do so at a lower rate but check the term you put it over. If you put the 24k over 10 years at 4%, the interest bill would be about 5k so it doesnt make sense in that circumstance. Also, if you include it in the mortgage, you cant claim interest relief on the 24k and also, some banks aren't too keen with refinancing short term debt into long term for what they consider 'living' expenses. In short, check your total interest calculated figure over various terms, at the various rates to make your decision.