What you REALLY want is a wind machine. Its different from a regular box fan in two ways. First, it pushes a lot more air through, so you can use it from farther away from the model (otherwise box fans end up being in the shot if its full length). Second, the wind is more focused, so its not blowing (wasting) wind all over the place. Most the fans I've seen in studios are longer and about a foot in diameter - kind of like a small thick cannon. Bowen makes a good one, you should check with any pro-oriented photo supply to buy one, but they're not cheap. They usually run $25-35/day just to rent. Otherwise you'll have to wait for summer I guess. (Not me though - it was 78 degress here in LA today!)
Regards,
Andy Pearlman
Andy Pearlman Studio