you should be fine, but as a rule, and so you know how to do it, work out the cubic ft or metres of the room, then get a fan that can suck 20 times that amount in an hour
So, in your case 6 x 3 x 2 = 36 cubic feet
x 20 = 720 cubic feet
So, you need a fan that can move 720 cubic ft (or 20...