I'm using a 60cm x 60cm x 140 cm grow tent, i've worked out the CFM my fan will need to be; about 20 CFM (adjusting for carbon filter), and i found an extractor fan on ebay that says it moves about that much, but it's only 60mm x 60mm and costs £4, i'm not entirely convinced a fan that small can vent my grow tent well enough but i',m no expert. I just wanted to know if i should get it or not?
You want to cycle your air several times per minute becausE one you get lights on there 20 cfm will not touch your heat. I would recommend at least 100 to 150 cfm if not more. There is a sticky about ventilation that goes more in depth. I think it is in the beginners section.