From the Bible:
...Look for an extraction fan with the capacity to change the air once every minute. Capacity refers to the amount of power need to circulate the air volume of your structure. Calculate the volume by multiplying the square footage of your greenhouse by the height. Multiply the volume by sixty air changes per hour to get the cfm capacity...

2ft x 8ft x 8ft x 60 minutes = 7680 cfm
Joedaddy Reviewed by Joedaddy on . Heat dissapation: How many CFM per Watt? come on theres gotta be a good way to caculat that shit Rating: 5