If the Greenwich study is right, ETF assets could double in the next two years. And not for the reason everybody thinks.

For the past few years, the talk of the town in the ETF industry has been the growth of the financial adviser market.

ETFs began as an institutional product. The first U.S. ETF, the S&P 500 SPDR (NYSEArca: SPY), was designed explicitly for the institutional market, and for years, the primary users of ETFs were institutions.

That started to change at the turn of the millennium, when ETF sponsors (led by iShares) began a massive education campaign designed to build out the financial adviser market. That effort was wildly successful, and today, most estimates suggest that 50 percent of all ETF assets are held by financial advisers.

The trend in the ETF industry has been to push the products further and further down the investor food chain, building the audience away from the institutional market toward a retail audience. ETF sponsors like iShares and State Street Global Advisers have said this year that they are beginning a new push targeting self-directed or retail investors, seeing that as the next wave of growth. This idea was picked up in a new white paper published recently by Cogent Research, which blared, “Self-Directed Investors Are Driving ETF Popularity and Growth.”

But a new institutional ETF survey published this week by Greenwich Associates, and reported on here by IndexUniverse.com, tells me that this exclusive focus on the retail market may be misplaced. The next massive wave of ETF growth could come not from retail but from a reinvigoration of the institutional marketplace.

The report surveyed 70 institutional investors and found that only 14 percent actually used ETFs. Fourteen percent! And yet, institutions collectively hold about $400 billion in U.S. ETF assets. It’s easy to do the math. A minor uptick in the number of institutional users—say, from 14 to 21 percent—could theoretically drive another $200 billion in assets.

The survey suggests that more than a minor uptick could be coming. As IndexUniverse reported, “[o]ver half of the 70 U.S. institutional investors Greenwich surveyed said their ETF use will increase in the next three years …”

What’s most curious is that 30 percent of those surveyed don’t use ETFs “because they lack familiarity with these instruments.” Educate that group and bring them into the fold, and you could easily see institutional ETF usage double.

It doesn’t take a lot of institutions to move the needle substantially on ETF assets. If the Greenwich survey is accurate, and if more institutions follow the lead of endowments like Harvard University and become big users of ETFs, we could see assets push into the trillions very quickly.