I own a few rental properties and I had similar dilemma up until a few months ago. My concern always had been that HELOCs are adjustable rate (mine is tied to prime rate) and was worried interest rates would shoot up and my interest cost would sky rocket. Then, one day a thought occurred that it is much more important to have a separate reserve set up in the form of diversified stock portfolio because if an emergency happened, such as a job loss, and I could not pay my monthly HELOC payment, I could potentially lose my properties, even though debt to value on the property is way below 50%. I do have a healthy emergency fund in savings that will last me about one year but that is for living expenses, not pay investment property HELOC. My properties also give off more in income than expenses but I've had situations where tenants move out and a new tenant would not move in for more 6 months. If job loss happened to coincide with vacancy, I could potentially get in trouble. For this reason, I put any excess funds I have into VOO, exchange traded S&P index, which has been up 13.6% over the last seven months. Once I have built up enough to pay off my HELOC, I intend to sell the ETF to repay the loan. But until then, I have cushion against any unforeseen cash flow problems.