For anybody wondering if the ETF industry is as hot as its ever been, consider the following numbers.U.S. listed ETFs saw inflows of $40.1 billion in January 2017. That's on top of the $61.5 billion that flowed into ETFs in December 2016.January's ETF net inflows were split relatively evenly between domestic equity ($15 billion), international equity ($12 billion) and fixed income ($12 billion).The Vanguard 500 Index Fund (VOO) was the biggest net beneficiary with inflows of $2.2 billion in January alone.Total ETF assets now sit at $2.64 trillion. The industry would need to average net inflows of about $33 billion per month for the remaining 11 months of 2017 to hit $3 trillion.Passively managed ETFs and mutual funds saw $504.8 billion of inflows in 2016. Conversely, actively managed funds saw net outflows of $340.1 billion.In 2016, Vanguard's actively managed funds saw more than $20 billion of net INFLOWS. Vanguard just can't seem to lose!85% of flows into ETFs in 2016 went to funds with an expense ratio of 0.09% or less.Comment below and let me know if you think we'll see ETFs hit $3 trillion in assets by the end of 2017.