When making this decision you should factor in a whole lot of other things as well (income, retirement, safety money, etc.) so I am not going to give you advice on that without knowing your situation.
However, my personal opinion on borrowing anything, in this case the heloc, is that you should have a clear plan in place to pay it back. I am assuming you are getting the HELOC for the down payment and that you are going to get traditional debt for the rest of your purchase.
A lot of people treat helocs like free cash and then get hurt when it is due. They buy properties that don't generate income but bank on appreciation to pay it back. That is gambling. Make sure the cash flows of the property can pay down the heloc for the term. If you can't pay the HELOC back by the end of the term, you may not have enough to refinance the property if you can't sell it and can't re-up the HELOC. This assumes that the property doesn't depreciate. Just really think about the worst case situation and if you still feel comfortable with it.