Circulating fans

[Carolina girl]

I'm trying to figure out what I should get for circulating fans in my greenhouse to ensure good air movement in the winter. It's been up for less than a year, and so far I've relied on some old box fans. But as I add more plants I know I'll need something more.

It's relatively large for a hobby greenhouse, 14' x 24' with 10' roof height at the center.

So far, after visiting 3 websites I have 3 different figures for the cfm rating I need for an overhead circulating fan, ranging from 1000 cfm to 4000 cfm. (!) I suspect the lower figure is closer to correct, since the third number I have is 1200 cfm.

I've seen advice to use two fans in diagonal corners (above the plants) to create an oval air circ pattern, which is similar to what I've seen in large production greenhouses. Also advice to aim fans up or down to break up stratification of warm air at the roof in the winter, but nothing on placement of fans for that.

Does anyone have good information on air circulation fans, particularly for use during the cooler months?

Thanks!
Ann