Brandon Turner says, "Using a home equity line of credit, popularly known as a HELOC, is one of my favorite creative strategies for investing in real estate."
Just be aware that the greater the leverage, the more risk you have going into any major real-estate downturn. The only thing that will keep you afloat are renters paying enough to meet your loan payments, etc. If a downturn slams the whole economy hard, you could have a hard time making payments. That's why old-school investors did better going into the Great Recession. They had more equity and lower loan payments.