You need a fan to evacuate 5 times the room volume in an hour.
Your room is roughly 6'x4'x2'..... so thats 6 feet x 4 feet= 24 square feet... 24 x2=48 cubic feet... so your room is 48 cubic feet..... 48 cubic feet x 5 total volumes of your room= 240 cubic feet, you'll need a fan at least this big.