Fans are rated by how many cubic feet per minute the fan is capable of cycling. You can determine the number of air changes per hour if you know the capacity of the fan, convert that figure to cubic feet per hour, and compare that to the volume of the room.
Measure the length, width and height of your room in feet. Multiply these three figures together to get an approximate figure for the number of cubic feet in your room. For example, if the room is 10 feet by 10 feet by 12 feet, there are about 1200 cubic feet of air to move in the room.
Check your owner's manual to determine the capacity of the fan in cubic feet per minute.
Multiply the capacity of your fan in cubic feet per minute by 60 to convert it to cubic feet per hour. For example, if your fan were capable of 200 cubic feet per minute, you multiply it by 60 to get 12,000 cubic feet per hour.
Divide this figure by the volume of the room to calculate the number of air changes per hour. Finishing the example, divide 12,000 cubic feet per hour by 1,200 cubic feet to find that you get 10 air changes per hour.